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 $58.51   4.227%   $60.9832   $60.98   $61.00   $61.00  
  Purchase #2 $137.37   4.389%   $143.3992   $143.40   $143.40   $143.40  
  Purchase #3 $115.90   13.515%   $131.5639   $131.56   $131.55   $131.60  
  Purchase #4 $140.43   6.593%   $149.6885   $149.69   $149.70   $149.70  
  Purchase #5 $127.55   5.817%   $134.9696   $134.97   $134.95   $135.00  
  Purchase #6 $224.64   11.298%   $250.0198   $250.02   $250.00   $250.00  
  Purchase #7 $161.95   12.512%   $182.2132   $182.21   $182.20   $182.20  
  7 purchase totals = $966.35       $1,052.8374   $1,052.83   $1,052.80   $1,052.90