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 $111.41   12.201%   $125.0031   $125.00   $125.00   $125.00  
  Purchase #2 $154.96   3.802%   $160.8516   $160.85   $160.85   $160.90  
  Purchase #3 $9.41   8.587%   $10.218   $10.22   $10.20   $10.20  
  Purchase #4 $153.90   7.219%   $165.01   $165.01   $165.00   $165.00  
  Purchase #5 $14.85   7.185%   $15.917   $15.92   $15.90   $15.90  
  Purchase #6 $112.27   3.741%   $116.47   $116.47   $116.45   $116.50  
  Purchase #7 $216.56   12.151%   $242.8742   $242.87   $242.85   $242.90  
  7 purchase totals = $773.36       $836.3439   $836.34   $836.25   $836.40