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 $87.59   6.788%   $93.5356   $93.54   $93.55   $93.50  
  Purchase #2 $77.29   8.318%   $83.719   $83.72   $83.70   $83.70  
  Purchase #3 $91.37   10.806%   $101.2434   $101.24   $101.25   $101.20  
  Purchase #4 $217.95   7.728%   $234.7932   $234.79   $234.80   $234.80  
  Purchase #5 $48.98   3.532%   $50.71   $50.71   $50.70   $50.70  
  Purchase #6 $151.35   4.656%   $158.3969   $158.40   $158.40   $158.40  
  Purchase #7 $212.57   6.729%   $226.8738   $226.87   $226.85   $226.90  
  7 purchase totals = $887.10       $949.2719   $949.27   $949.25   $949.20