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 $125.61   3.643%   $130.186   $130.19   $130.20   $130.20  
  Purchase #2 $231.94   5.836%   $245.476   $245.48   $245.50   $245.50  
  Purchase #3 $152.33   4.144%   $158.6426   $158.64   $158.65   $158.60  
  Purchase #4 $82.69   9.772%   $90.7705   $90.77   $90.75   $90.80  
  Purchase #5 $206.70   3.497%   $213.9283   $213.93   $213.95   $213.90  
  Purchase #6 $47.55   13.454%   $53.9474   $53.95   $53.95   $53.90  
  Purchase #7 $59.87   5.188%   $62.9761   $62.98   $63.00   $63.00  
  7 purchase totals = $906.69       $955.9269   $955.94   $956.00   $955.90