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 $119.47   12.781%   $134.7395   $134.74   $134.75   $134.70  
  Purchase #2 $20.97   11.474%   $23.3761   $23.38   $23.40   $23.40  
  Purchase #3 $25.92   7.852%   $27.9552   $27.96   $27.95   $28.00  
  Purchase #4 $97.79   4.135%   $101.8336   $101.83   $101.85   $101.80  
  Purchase #5 $182.89   5.527%   $192.9983   $193.00   $193.00   $193.00  
  Purchase #6 $206.44   8.792%   $224.5902   $224.59   $224.60   $224.60  
  Purchase #7 $60.86   12.113%   $68.232   $68.23   $68.25   $68.20  
  7 purchase totals = $714.34       $773.7249   $773.73   $773.80   $773.70