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 $54.52   12.504%   $61.3372   $61.34   $61.35   $61.30  
  Purchase #2 $20.86   11.618%   $23.2835   $23.28   $23.30   $23.30  
  Purchase #3 $26.64   6.312%   $28.3215   $28.32   $28.30   $28.30  
  Purchase #4 $185.48   13.793%   $211.0633   $211.06   $211.05   $211.10  
  Purchase #5 $95.47   3.366%   $98.6835   $98.68   $98.70   $98.70  
  Purchase #6 $192.27   8.163%   $207.965   $207.97   $207.95   $208.00  
  Purchase #7 $85.45   11.690%   $95.4391   $95.44   $95.45   $95.40  
  7 purchase totals = $660.69       $726.0931   $726.09   $726.10   $726.10