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 $111.95   11.427%   $124.7425   $124.74   $124.75   $124.70  
  Purchase #2 $210.54   12.300%   $236.4364   $236.44   $236.45   $236.40  
  Purchase #3 $97.38   7.404%   $104.59   $104.59   $104.60   $104.60  
  Purchase #4 $45.92   13.643%   $52.1849   $52.18   $52.20   $52.20  
  Purchase #5 $24.34   13.126%   $27.5349   $27.53   $27.55   $27.50  
  Purchase #6 $250.93   6.170%   $266.4124   $266.41   $266.40   $266.40  
  Purchase #7 $242.92   12.107%   $272.3303   $272.33   $272.35   $272.30  
  7 purchase totals = $983.98       $1,084.2314   $1,084.22   $1,084.30   $1,084.10