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 $84.29   12.153%   $94.5338   $94.53   $94.55   $94.50  
  Purchase #2 $60.50   10.698%   $66.9723   $66.97   $66.95   $67.00  
  Purchase #3 $14.28   7.745%   $15.386   $15.39   $15.40   $15.40  
  Purchase #4 $83.65   13.758%   $95.1586   $95.16   $95.15   $95.20  
  Purchase #5 $74.65   4.656%   $78.1257   $78.13   $78.15   $78.10  
  Purchase #6 $211.27   5.606%   $223.1138   $223.11   $223.10   $223.10  
  Purchase #7 $129.95   12.522%   $146.2223   $146.22   $146.20   $146.20  
  7 purchase totals = $658.59       $719.5125   $719.51   $719.50   $719.50