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 $60.44   5.810%   $63.9516   $63.95   $63.95   $64.00  
  Purchase #2 $207.97   12.809%   $234.6089   $234.61   $234.60   $234.60  
  Purchase #3 $53.49   10.333%   $59.0171   $59.02   $59.00   $59.00  
  Purchase #4 $105.91   9.655%   $116.1356   $116.14   $116.15   $116.10  
  Purchase #5 $154.60   7.666%   $166.4516   $166.45   $166.45   $166.50  
  Purchase #6 $60.65   9.646%   $66.5003   $66.50   $66.50   $66.50  
  Purchase #7 $245.34   4.868%   $257.2832   $257.28   $257.30   $257.30  
  7 purchase totals = $888.40       $963.9483   $963.95   $963.95   $964.00