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 $32.95   7.511%   $35.4249   $35.42   $35.40   $35.40  
  Purchase #2 $98.34   10.600%   $108.764   $108.76   $108.75   $108.80  
  Purchase #3 $154.77   13.668%   $175.924   $175.92   $175.90   $175.90  
  Purchase #4 $109.25   9.572%   $119.7074   $119.71   $119.70   $119.70  
  Purchase #5 $111.37   13.615%   $126.533   $126.53   $126.55   $126.50  
  Purchase #6 $32.47   12.372%   $36.4872   $36.49   $36.50   $36.50  
  Purchase #7 $138.33   13.129%   $156.4913   $156.49   $156.50   $156.50  
  7 purchase totals = $677.48       $759.3318   $759.32   $759.30   $759.30