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 $93.89   13.612%   $106.6703   $106.67   $106.65   $106.70  
  Purchase #2 $224.47   11.485%   $250.2504   $250.25   $250.25   $250.30  
  Purchase #3 $5.27   10.726%   $5.8353   $5.84   $5.85   $5.80  
  Purchase #4 $89.81   11.684%   $100.3034   $100.30   $100.30   $100.30  
  Purchase #5 $65.80   10.756%   $72.8774   $72.88   $72.90   $72.90  
  Purchase #6 $202.99   5.523%   $214.2011   $214.20   $214.20   $214.20  
  Purchase #7 $126.74   4.411%   $132.3305   $132.33   $132.35   $132.30  
  7 purchase totals = $808.97       $882.4684   $882.47   $882.50   $882.50