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 $96.63   5.422%   $101.8693   $101.87   $101.85   $101.90  
  Purchase #2 $102.38   6.110%   $108.6354   $108.64   $108.65   $108.60  
  Purchase #3 $129.69   5.548%   $136.8852   $136.89   $136.90   $136.90  
  Purchase #4 $101.79   12.462%   $114.4751   $114.48   $114.50   $114.50  
  Purchase #5 $13.51   10.518%   $14.931   $14.93   $14.95   $14.90  
  Purchase #6 $33.55   5.363%   $35.3493   $35.35   $35.35   $35.30  
  Purchase #7 $216.46   11.256%   $240.8247   $240.82   $240.80   $240.80  
  7 purchase totals = $694.01       $752.9700   $752.98   $753.00   $752.90