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 $248.37   10.823%   $275.2511   $275.25   $275.25   $275.30  
  Purchase #2 $91.62   4.211%   $95.4781   $95.48   $95.50   $95.50  
  Purchase #3 $104.85   13.282%   $118.7762   $118.78   $118.80   $118.80  
  Purchase #4 $148.27   4.102%   $154.352   $154.35   $154.35   $154.40  
  Purchase #5 $147.95   7.331%   $158.7962   $158.80   $158.80   $158.80  
  Purchase #6 $87.91   11.588%   $98.097   $98.10   $98.10   $98.10  
  Purchase #7 $46.67   9.197%   $50.9622   $50.96   $50.95   $51.00  
  7 purchase totals = $875.64       $951.7128   $951.72   $951.75   $951.90