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 $57.84   8.167%   $62.5638   $62.56   $62.55   $62.60  
  Purchase #2 $144.57   9.616%   $158.4719   $158.47   $158.45   $158.50  
  Purchase #3 $37.84   4.132%   $39.4035   $39.40   $39.40   $39.40  
  Purchase #4 $92.55   13.428%   $104.9776   $104.98   $105.00   $105.00  
  Purchase #5 $192.40   8.581%   $208.9098   $208.91   $208.90   $208.90  
  Purchase #6 $143.59   7.423%   $154.2487   $154.25   $154.25   $154.20  
  Purchase #7 $71.94   3.541%   $74.4874   $74.49   $74.50   $74.50  
  7 purchase totals = $740.73       $803.0627   $803.06   $803.05   $803.10