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 $45.95   9.357%   $50.2495   $50.25   $50.25   $50.20  
  Purchase #2 $151.26   6.203%   $160.6427   $160.64   $160.65   $160.60  
  Purchase #3 $227.34   6.508%   $242.1353   $242.14   $242.15   $242.10  
  Purchase #4 $113.96   11.116%   $126.6278   $126.63   $126.65   $126.60  
  Purchase #5 $85.75   11.871%   $95.9294   $95.93   $95.95   $95.90  
  Purchase #6 $89.76   9.567%   $98.3473   $98.35   $98.35   $98.30  
  Purchase #7 $168.54   11.413%   $187.7755   $187.78   $187.80   $187.80  
  7 purchase totals = $882.56       $961.7075   $961.72   $961.80   $961.50