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 $91.47   4.189%   $95.3017   $95.30   $95.30   $95.30  
  Purchase #2 $30.99   10.224%   $34.1584   $34.16   $34.15   $34.20  
  Purchase #3 $91.25   6.525%   $97.2041   $97.20   $97.20   $97.20  
  Purchase #4 $221.40   9.644%   $242.7518   $242.75   $242.75   $242.80  
  Purchase #5 $54.50   11.265%   $60.6394   $60.64   $60.65   $60.60  
  Purchase #6 $212.85   12.797%   $240.0884   $240.09   $240.10   $240.10  
  Purchase #7 $146.81   4.302%   $153.1258   $153.13   $153.15   $153.10  
  7 purchase totals = $849.27       $923.2696   $923.27   $923.30   $923.30