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 $124.42   13.519%   $141.2403   $141.24   $141.25   $141.20  
  Purchase #2 $83.99   4.103%   $87.4361   $87.44   $87.45   $87.40  
  Purchase #3 $83.54   13.629%   $94.9257   $94.93   $94.95   $94.90  
  Purchase #4 $142.81   10.333%   $157.5666   $157.57   $157.55   $157.60  
  Purchase #5 $108.51   7.803%   $116.977   $116.98   $117.00   $117.00  
  Purchase #6 $59.61   11.271%   $66.3286   $66.33   $66.35   $66.30  
  Purchase #7 $133.29   12.817%   $150.3738   $150.37   $150.35   $150.40  
  7 purchase totals = $736.17       $814.8481   $814.86   $814.90   $814.80