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 $194.42   6.389%   $206.8415   $206.84   $206.85   $206.80  
  Purchase #2 $9.34   9.548%   $10.2318   $10.23   $10.25   $10.20  
  Purchase #3 $250.37   13.570%   $284.3452   $284.35   $284.35   $284.30  
  Purchase #4 $91.66   4.558%   $95.8379   $95.84   $95.85   $95.80  
  Purchase #5 $199.66   7.788%   $215.2095   $215.21   $215.20   $215.20  
  Purchase #6 $41.92   5.415%   $44.19   $44.19   $44.20   $44.20  
  Purchase #7 $24.87   10.501%   $27.4816   $27.48   $27.50   $27.50  
  7 purchase totals = $812.24       $884.1375   $884.14   $884.20   $884.00