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 $130.55   12.206%   $146.4849   $146.48   $146.50   $146.50  
  Purchase #2 $44.84   4.526%   $46.8695   $46.87   $46.85   $46.90  
  Purchase #3 $8.68   5.639%   $9.1695   $9.17   $9.15   $9.20  
  Purchase #4 $248.61   5.633%   $262.6142   $262.61   $262.60   $262.60  
  Purchase #5 $185.55   8.294%   $200.9395   $200.94   $200.95   $200.90  
  Purchase #6 $196.61   12.618%   $221.4182   $221.42   $221.40   $221.40  
  Purchase #7 $139.31   6.719%   $148.6702   $148.67   $148.65   $148.70  
  7 purchase totals = $954.15       $1,036.1660   $1,036.16   $1,036.10   $1,036.20