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 $125.92   6.674%   $134.3239   $134.32   $134.30   $134.30  
  Purchase #2 $157.31   7.481%   $169.0784   $169.08   $169.10   $169.10  
  Purchase #3 $167.35   12.562%   $188.3725   $188.37   $188.35   $188.40  
  Purchase #4 $101.70   4.345%   $106.1189   $106.12   $106.10   $106.10  
  Purchase #5 $242.72   10.494%   $268.191   $268.19   $268.20   $268.20  
  Purchase #6 $71.94   6.526%   $76.6348   $76.63   $76.65   $76.60  
  Purchase #7 $69.31   13.461%   $78.6398   $78.64   $78.65   $78.60  
  7 purchase totals = $936.25       $1,021.3593   $1,021.35   $1,021.35   $1,021.30