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 $58.76   9.421%   $64.2958   $64.30   $64.30   $64.30  
  Purchase #2 $141.38   9.179%   $154.3573   $154.36   $154.35   $154.40  
  Purchase #3 $210.66   10.406%   $232.5813   $232.58   $232.60   $232.60  
  Purchase #4 $41.86   10.306%   $46.1741   $46.17   $46.15   $46.20  
  Purchase #5 $164.35   3.672%   $170.3849   $170.38   $170.40   $170.40  
  Purchase #6 $154.29   12.618%   $173.7583   $173.76   $173.75   $173.80  
  Purchase #7 $28.36   9.103%   $30.9416   $30.94   $30.95   $30.90  
  7 purchase totals = $799.66       $872.4933   $872.49   $872.50   $872.60