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 $22.72   8.254%   $24.5953   $24.60   $24.60   $24.60  
  Purchase #2 $86.95   11.760%   $97.1753   $97.18   $97.20   $97.20  
  Purchase #3 $244.47   12.616%   $275.3123   $275.31   $275.30   $275.30  
  Purchase #4 $233.91   4.616%   $244.7073   $244.71   $244.70   $244.70  
  Purchase #5 $68.88   8.241%   $74.5564   $74.56   $74.55   $74.60  
  Purchase #6 $53.87   6.250%   $57.2369   $57.24   $57.25   $57.20  
  Purchase #7 $94.36   8.230%   $102.1258   $102.13   $102.15   $102.10  
  7 purchase totals = $805.16       $875.7093   $875.73   $875.75   $875.70