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 $217.76   6.821%   $232.6134   $232.61   $232.60   $232.60  
  Purchase #2 $242.89   9.262%   $265.3865   $265.39   $265.40   $265.40  
  Purchase #3 $27.52   13.154%   $31.14   $31.14   $31.15   $31.10  
  Purchase #4 $180.55   8.288%   $195.514   $195.51   $195.50   $195.50  
  Purchase #5 $227.96   13.251%   $258.167   $258.17   $258.15   $258.20  
  Purchase #6 $209.92   11.744%   $234.573   $234.57   $234.55   $234.60  
  Purchase #7 $113.62   3.799%   $117.9364   $117.94   $117.95   $117.90  
  7 purchase totals = $1,220.22       $1,335.3303   $1,335.33   $1,335.30   $1,335.30