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 $244.33   7.598%   $262.8942   $262.89   $262.90   $262.90  
  Purchase #2 $202.60   10.342%   $223.5529   $223.55   $223.55   $223.60  
  Purchase #3 $157.81   3.673%   $163.6064   $163.61   $163.60   $163.60  
  Purchase #4 $70.68   8.403%   $76.6192   $76.62   $76.60   $76.60  
  Purchase #5 $131.94   5.766%   $139.5477   $139.55   $139.55   $139.50  
  Purchase #6 $146.92   8.110%   $158.8352   $158.84   $158.85   $158.80  
  Purchase #7 $7.64   9.385%   $8.357   $8.36   $8.35   $8.40  
  7 purchase totals = $961.92       $1,033.4126   $1,033.42   $1,033.40   $1,033.40