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 $61.62   12.567%   $69.3638   $69.36   $69.35   $69.40  
  Purchase #2 $120.90   4.476%   $126.3115   $126.31   $126.30   $126.30  
  Purchase #3 $29.84   3.708%   $30.9465   $30.95   $30.95   $30.90  
  Purchase #4 $234.28   13.559%   $266.046   $266.05   $266.05   $266.00  
  Purchase #5 $62.41   9.419%   $68.2884   $68.29   $68.30   $68.30  
  Purchase #6 $230.48   12.864%   $260.1289   $260.13   $260.15   $260.10  
  Purchase #7 $125.90   6.861%   $134.538   $134.54   $134.55   $134.50  
  7 purchase totals = $865.43       $955.6231   $955.63   $955.65   $955.50