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 $42.34   4.599%   $44.2872   $44.29   $44.30   $44.30  
  Purchase #2 $194.94   6.681%   $207.9639   $207.96   $207.95   $208.00  
  Purchase #3 $75.28   4.183%   $78.429   $78.43   $78.45   $78.40  
  Purchase #4 $175.52   8.584%   $190.5866   $190.59   $190.60   $190.60  
  Purchase #5 $63.93   4.580%   $66.858   $66.86   $66.85   $66.90  
  Purchase #6 $121.80   3.415%   $125.9595   $125.96   $125.95   $126.00  
  Purchase #7 $48.88   6.741%   $52.175   $52.18   $52.20   $52.20  
  7 purchase totals = $722.69       $766.2592   $766.27   $766.30   $766.40