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 $248.35   5.703%   $262.5134   $262.51   $262.50   $262.50  
  Purchase #2 $51.59   7.816%   $55.6223   $55.62   $55.60   $55.60  
  Purchase #3 $54.73   13.565%   $62.1541   $62.15   $62.15   $62.20  
  Purchase #4 $124.78   7.146%   $133.6968   $133.70   $133.70   $133.70  
  Purchase #5 $100.53   11.410%   $112.0005   $112.00   $112.00   $112.00  
  Purchase #6 $173.25   5.279%   $182.3959   $182.40   $182.40   $182.40  
  Purchase #7 $12.43   12.317%   $13.961   $13.96   $13.95   $14.00  
  7 purchase totals = $765.66       $822.3440   $822.34   $822.30   $822.40