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 $93.47   5.341%   $98.4622   $98.46   $98.45   $98.50  
  Purchase #2 $124.94   8.341%   $135.3612   $135.36   $135.35   $135.40  
  Purchase #3 $220.92   7.174%   $236.7688   $236.77   $236.75   $236.80  
  Purchase #4 $13.63   8.617%   $14.8045   $14.80   $14.80   $14.80  
  Purchase #5 $146.69   9.647%   $160.8412   $160.84   $160.85   $160.80  
  Purchase #6 $68.88   3.363%   $71.1964   $71.20   $71.20   $71.20  
  Purchase #7 $25.47   12.613%   $28.6825   $28.68   $28.70   $28.70  
  7 purchase totals = $694.00       $746.1168   $746.11   $746.10   $746.20