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 $239.84   10.759%   $265.6444   $265.64   $265.65   $265.60  
  Purchase #2 $184.92   13.428%   $209.7511   $209.75   $209.75   $209.80  
  Purchase #3 $120.70   4.295%   $125.8841   $125.88   $125.90   $125.90  
  Purchase #4 $172.43   13.350%   $195.4494   $195.45   $195.45   $195.40  
  Purchase #5 $167.88   5.534%   $177.1705   $177.17   $177.15   $177.20  
  Purchase #6 $221.97   10.181%   $244.5688   $244.57   $244.55   $244.60  
  Purchase #7 $132.43   12.669%   $149.2076   $149.21   $149.20   $149.20  
  7 purchase totals = $1,240.17       $1,367.6759   $1,367.67   $1,367.65   $1,367.70