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 $131.91   6.262%   $140.1702   $140.17   $140.15   $140.20  
  Purchase #2 $199.91   6.468%   $212.8402   $212.84   $212.85   $212.80  
  Purchase #3 $58.57   11.209%   $65.1351   $65.14   $65.15   $65.10  
  Purchase #4 $205.81   5.743%   $217.6297   $217.63   $217.65   $217.60  
  Purchase #5 $241.70   13.456%   $274.2232   $274.22   $274.20   $274.20  
  Purchase #6 $65.50   4.451%   $68.4154   $68.42   $68.40   $68.40  
  Purchase #7 $162.63   13.416%   $184.4484   $184.45   $184.45   $184.40  
  7 purchase totals = $1,066.03       $1,162.8622   $1,162.87   $1,162.85   $1,162.70