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 $10.76   6.458%   $11.4549   $11.45   $11.45   $11.50  
  Purchase #2 $94.63   4.427%   $98.8193   $98.82   $98.80   $98.80  
  Purchase #3 $220.78   12.195%   $247.7041   $247.70   $247.70   $247.70  
  Purchase #4 $217.43   10.677%   $240.645   $240.65   $240.65   $240.60  
  Purchase #5 $92.63   6.660%   $98.7992   $98.80   $98.80   $98.80  
  Purchase #6 $218.93   4.271%   $228.2805   $228.28   $228.30   $228.30  
  Purchase #7 $18.41   3.267%   $19.0115   $19.01   $19.00   $19.00  
  7 purchase totals = $873.57       $944.7145   $944.71   $944.70   $944.70