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 $50.60   10.692%   $56.0102   $56.01   $56.00   $56.00  
  Purchase #2 $124.96   9.748%   $137.1411   $137.14   $137.15   $137.10  
  Purchase #3 $166.47   11.862%   $186.2167   $186.22   $186.20   $186.20  
  Purchase #4 $242.49   5.283%   $255.3007   $255.30   $255.30   $255.30  
  Purchase #5 $191.71   6.271%   $203.7321   $203.73   $203.75   $203.70  
  Purchase #6 $95.56   5.754%   $101.0585   $101.06   $101.05   $101.10  
  Purchase #7 $17.54   4.713%   $18.3667   $18.37   $18.35   $18.40  
  7 purchase totals = $889.33       $957.8260   $957.83   $957.80   $957.80