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 $30.53   11.681%   $34.0962   $34.10   $34.10   $34.10  
  Purchase #2 $220.87   7.369%   $237.1459   $237.15   $237.15   $237.10  
  Purchase #3 $153.56   8.721%   $166.952   $166.95   $166.95   $167.00  
  Purchase #4 $234.45   4.305%   $244.5431   $244.54   $244.55   $244.50  
  Purchase #5 $148.95   6.485%   $158.6094   $158.61   $158.60   $158.60  
  Purchase #6 $208.50   3.418%   $215.6265   $215.63   $215.65   $215.60  
  Purchase #7 $201.30   6.124%   $213.6276   $213.63   $213.65   $213.60  
  7 purchase totals = $1,198.16       $1,270.6007   $1,270.61   $1,270.65   $1,270.50