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 $118.62   12.407%   $133.3372   $133.34   $133.35   $133.30  
  Purchase #2 $124.83   9.163%   $136.2682   $136.27   $136.25   $136.30  
  Purchase #3 $163.64   11.366%   $182.2393   $182.24   $182.25   $182.20  
  Purchase #4 $20.73   13.146%   $23.4552   $23.46   $23.45   $23.50  
  Purchase #5 $63.42   9.723%   $69.5863   $69.59   $69.60   $69.60  
  Purchase #6 $185.33   12.291%   $208.1089   $208.11   $208.10   $208.10  
  Purchase #7 $173.59   13.810%   $197.5628   $197.56   $197.55   $197.60  
  7 purchase totals = $850.16       $950.5579   $950.57   $950.55   $950.60