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 $58.52   8.412%   $63.4427   $63.44   $63.45   $63.40  
  Purchase #2 $231.85   7.726%   $249.7627   $249.76   $249.75   $249.80  
  Purchase #3 $168.62   11.791%   $188.502   $188.50   $188.50   $188.50  
  Purchase #4 $88.90   8.218%   $96.2058   $96.21   $96.20   $96.20  
  Purchase #5 $111.30   13.627%   $126.4669   $126.47   $126.45   $126.50  
  Purchase #6 $76.81   9.827%   $84.3581   $84.36   $84.35   $84.40  
  Purchase #7 $118.77   11.521%   $132.4535   $132.45   $132.45   $132.50  
  7 purchase totals = $854.77       $941.1917   $941.19   $941.15   $941.30