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 $64.58   13.625%   $73.379   $73.38   $73.40   $73.40  
  Purchase #2 $177.27   6.498%   $188.789   $188.79   $188.80   $188.80  
  Purchase #3 $93.58   13.241%   $105.9709   $105.97   $105.95   $106.00  
  Purchase #4 $154.78   10.708%   $171.3538   $171.35   $171.35   $171.40  
  Purchase #5 $9.32   10.133%   $10.2644   $10.26   $10.25   $10.30  
  Purchase #6 $240.48   10.292%   $265.2302   $265.23   $265.25   $265.20  
  Purchase #7 $126.99   6.427%   $135.1516   $135.15   $135.15   $135.20  
  7 purchase totals = $867.00       $950.1389   $950.13   $950.15   $950.30