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 $140.55   8.103%   $151.9388   $151.94   $151.95   $151.90  
  Purchase #2 $50.56   4.227%   $52.6972   $52.70   $52.70   $52.70  
  Purchase #3 $158.95   13.824%   $180.9232   $180.92   $180.90   $180.90  
  Purchase #4 $203.31   5.634%   $214.7645   $214.76   $214.75   $214.80  
  Purchase #5 $104.29   12.816%   $117.6558   $117.66   $117.65   $117.70  
  Purchase #6 $61.43   4.195%   $64.007   $64.01   $64.00   $64.00  
  Purchase #7 $90.80   3.854%   $94.2994   $94.30   $94.30   $94.30  
  7 purchase totals = $809.89       $876.2859   $876.29   $876.25   $876.30