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 $232.78   7.373%   $249.9429   $249.94   $249.95   $249.90  
  Purchase #2 $97.33   7.231%   $104.3679   $104.37   $104.35   $104.40  
  Purchase #3 $111.59   12.825%   $125.9014   $125.90   $125.90   $125.90  
  Purchase #4 $236.94   4.313%   $247.1592   $247.16   $247.15   $247.20  
  Purchase #5 $172.95   6.491%   $184.1762   $184.18   $184.20   $184.20  
  Purchase #6 $91.32   8.697%   $99.2621   $99.26   $99.25   $99.30  
  Purchase #7 $39.84   12.772%   $44.9284   $44.93   $44.95   $44.90  
  7 purchase totals = $982.75       $1,055.7381   $1,055.74   $1,055.75   $1,055.80