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 $124.88   13.693%   $141.9798   $141.98   $142.00   $142.00  
  Purchase #2 $167.93   5.425%   $177.0402   $177.04   $177.05   $177.00  
  Purchase #3 $38.26   5.544%   $40.3811   $40.38   $40.40   $40.40  
  Purchase #4 $170.45   7.225%   $182.765   $182.77   $182.75   $182.80  
  Purchase #5 $140.63   6.456%   $149.7091   $149.71   $149.70   $149.70  
  Purchase #6 $92.49   5.668%   $97.7323   $97.73   $97.75   $97.70  
  Purchase #7 $144.62   4.720%   $151.4461   $151.45   $151.45   $151.40  
  7 purchase totals = $879.26       $941.0536   $941.06   $941.10   $941.00