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 $111.95   6.710%   $119.4618   $119.46   $119.45   $119.50  
  Purchase #2 $198.77   3.626%   $205.9774   $205.98   $206.00   $206.00  
  Purchase #3 $89.95   9.132%   $98.1642   $98.16   $98.15   $98.20  
  Purchase #4 $212.64   7.450%   $228.4817   $228.48   $228.50   $228.50  
  Purchase #5 $63.29   13.762%   $72   $72.00   $72.00   $72.00  
  Purchase #6 $191.25   6.426%   $203.5397   $203.54   $203.55   $203.50  
  Purchase #7 $239.61   9.132%   $261.4912   $261.49   $261.50   $261.50  
  7 purchase totals = $1,107.46       $1,189.1160   $1,189.11   $1,189.15   $1,189.20