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 $205.42   8.166%   $222.1946   $222.19   $222.20   $222.20  
  Purchase #2 $203.84   11.687%   $227.6628   $227.66   $227.65   $227.70  
  Purchase #3 $125.51   12.637%   $141.3707   $141.37   $141.35   $141.40  
  Purchase #4 $194.72   10.632%   $215.4226   $215.42   $215.40   $215.40  
  Purchase #5 $23.73   13.374%   $26.9037   $26.90   $26.90   $26.90  
  Purchase #6 $119.67   12.747%   $134.9243   $134.92   $134.90   $134.90  
  Purchase #7 $174.82   13.355%   $198.1672   $198.17   $198.15   $198.20  
  7 purchase totals = $1,047.71       $1,166.6459   $1,166.63   $1,166.55   $1,166.70