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 $183.74   6.169%   $195.0749   $195.07   $195.05   $195.10  
  Purchase #2 $111.49   12.133%   $125.0171   $125.02   $125.00   $125.00  
  Purchase #3 $103.37   12.642%   $116.438   $116.44   $116.45   $116.40  
  Purchase #4 $78.67   4.484%   $82.1976   $82.20   $82.20   $82.20  
  Purchase #5 $74.80   8.387%   $81.0735   $81.07   $81.05   $81.10  
  Purchase #6 $56.25   8.397%   $60.9733   $60.97   $60.95   $61.00  
  Purchase #7 $130.60   5.426%   $137.6864   $137.69   $137.70   $137.70  
  7 purchase totals = $738.92       $798.4608   $798.46   $798.40   $798.50