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 $118.53   11.874%   $132.6043   $132.60   $132.60   $132.60  
  Purchase #2 $213.95   6.451%   $227.7519   $227.75   $227.75   $227.80  
  Purchase #3 $50.91   11.222%   $56.6231   $56.62   $56.60   $56.60  
  Purchase #4 $81.98   4.135%   $85.3699   $85.37   $85.35   $85.40  
  Purchase #5 $167.80   12.773%   $189.2331   $189.23   $189.25   $189.20  
  Purchase #6 $129.54   10.814%   $143.5485   $143.55   $143.55   $143.50  
  Purchase #7 $68.34   13.311%   $77.4367   $77.44   $77.45   $77.40  
  7 purchase totals = $831.05       $912.5675   $912.56   $912.55   $912.50