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 $54.99   7.785%   $59.271   $59.27   $59.25   $59.30  
  Purchase #2 $93.56   3.806%   $97.1209   $97.12   $97.10   $97.10  
  Purchase #3 $108.92   8.240%   $117.895   $117.90   $117.90   $117.90  
  Purchase #4 $69.30   8.333%   $75.0748   $75.07   $75.05   $75.10  
  Purchase #5 $173.76   13.355%   $196.9656   $196.97   $196.95   $197.00  
  Purchase #6 $141.49   9.701%   $155.2159   $155.22   $155.20   $155.20  
  Purchase #7 $211.79   9.271%   $231.4251   $231.43   $231.45   $231.40  
  7 purchase totals = $853.81       $932.9683   $932.98   $932.90   $933.00