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 $246.37   7.579%   $265.0424   $265.04   $265.05   $265.00  
  Purchase #2 $222.75   13.818%   $253.5296   $253.53   $253.55   $253.50  
  Purchase #3 $27.35   12.783%   $30.8462   $30.85   $30.85   $30.80  
  Purchase #4 $187.47   3.589%   $194.1983   $194.20   $194.20   $194.20  
  Purchase #5 $94.29   4.608%   $98.6349   $98.63   $98.65   $98.60  
  Purchase #6 $86.36   12.761%   $97.3804   $97.38   $97.40   $97.40  
  Purchase #7 $36.58   5.358%   $38.54   $38.54   $38.55   $38.50  
  7 purchase totals = $901.17       $978.1718   $978.17   $978.25   $978.00