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 $141.89   7.716%   $152.8382   $152.84   $152.85   $152.80  
  Purchase #2 $199.87   10.247%   $220.3507   $220.35   $220.35   $220.40  
  Purchase #3 $161.45   7.684%   $173.8558   $173.86   $173.85   $173.90  
  Purchase #4 $143.63   9.819%   $157.733   $157.73   $157.75   $157.70  
  Purchase #5 $91.91   5.718%   $97.1654   $97.17   $97.15   $97.20  
  Purchase #6 $141.46   5.714%   $149.543   $149.54   $149.55   $149.50  
  Purchase #7 $54.96   13.296%   $62.2675   $62.27   $62.25   $62.30  
  7 purchase totals = $935.17       $1,013.7536   $1,013.76   $1,013.75   $1,013.80