Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $58.90   11.610%   $65.7383   $65.74   $65.75   $65.70  
  Purchase #2 $146.46   10.499%   $161.8368   $161.84   $161.85   $161.80  
  Purchase #3 $179.49   3.696%   $186.124   $186.12   $186.10   $186.10  
  Purchase #4 $221.75   12.459%   $249.3778   $249.38   $249.40   $249.40  
  Purchase #5 $53.44   12.498%   $60.1189   $60.12   $60.10   $60.10  
  Purchase #6 $53.74   8.777%   $58.4568   $58.46   $58.45   $58.50  
  Purchase #7 $222.74   10.351%   $245.7958   $245.80   $245.80   $245.80  
  7 purchase totals = $936.52       $1,027.4484   $1,027.46   $1,027.45   $1,027.40