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 $135.51   9.588%   $148.5027   $148.50   $148.50   $148.50  
  Purchase #2 $185.60   5.285%   $195.409   $195.41   $195.40   $195.40  
  Purchase #3 $182.55   4.542%   $190.8414   $190.84   $190.85   $190.80  
  Purchase #4 $81.57   4.152%   $84.9568   $84.96   $84.95   $85.00  
  Purchase #5 $201.72   12.316%   $226.5638   $226.56   $226.55   $226.60  
  Purchase #6 $126.66   9.823%   $139.1018   $139.10   $139.10   $139.10  
  Purchase #7 $140.34   9.693%   $153.9432   $153.94   $153.95   $153.90  
  7 purchase totals = $1,053.95       $1,139.3187   $1,139.31   $1,139.30   $1,139.30