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 $22.29   11.845%   $24.9303   $24.93   $24.95   $24.90  
  Purchase #2 $201.38   10.805%   $223.1391   $223.14   $223.15   $223.10  
  Purchase #3 $211.35   5.140%   $222.2134   $222.21   $222.20   $222.20  
  Purchase #4 $170.45   9.584%   $186.7859   $186.79   $186.80   $186.80  
  Purchase #5 $45.82   4.850%   $48.0423   $48.04   $48.05   $48.00  
  Purchase #6 $104.95   7.231%   $112.5389   $112.54   $112.55   $112.50  
  Purchase #7 $119.75   11.423%   $133.429   $133.43   $133.45   $133.40  
  7 purchase totals = $875.99       $951.0789   $951.08   $951.15   $950.90