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 $24.60   9.181%   $26.8585   $26.86   $26.85   $26.90  
  Purchase #2 $200.92   5.272%   $211.5125   $211.51   $211.50   $211.50  
  Purchase #3 $44.46   6.607%   $47.3975   $47.40   $47.40   $47.40  
  Purchase #4 $109.54   9.155%   $119.5684   $119.57   $119.55   $119.60  
  Purchase #5 $244.49   13.562%   $277.6477   $277.65   $277.65   $277.60  
  Purchase #6 $5.95   9.873%   $6.5374   $6.54   $6.55   $6.50  
  Purchase #7 $102.27   12.553%   $115.108   $115.11   $115.10   $115.10  
  7 purchase totals = $732.23       $804.6300   $804.64   $804.60   $804.60