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 $67.61   13.638%   $76.8307   $76.83   $76.85   $76.80  
  Purchase #2 $205.29   8.261%   $222.249   $222.25   $222.25   $222.20  
  Purchase #3 $183.55   7.603%   $197.5053   $197.51   $197.50   $197.50  
  Purchase #4 $79.35   3.726%   $82.3066   $82.31   $82.30   $82.30  
  Purchase #5 $119.29   7.726%   $128.5063   $128.51   $128.50   $128.50  
  Purchase #6 $181.32   11.158%   $201.5517   $201.55   $201.55   $201.60  
  Purchase #7 $30.68   13.277%   $34.7534   $34.75   $34.75   $34.80  
  7 purchase totals = $867.09       $943.7030   $943.71   $943.70   $943.70