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 $41.25   12.286%   $46.318   $46.32   $46.30   $46.30  
  Purchase #2 $227.86   3.819%   $236.562   $236.56   $236.55   $236.60  
  Purchase #3 $21.31   10.387%   $23.5235   $23.52   $23.50   $23.50  
  Purchase #4 $54.37   8.535%   $59.0105   $59.01   $59.00   $59.00  
  Purchase #5 $113.97   10.634%   $126.0896   $126.09   $126.10   $126.10  
  Purchase #6 $25.69   9.105%   $28.0291   $28.03   $28.05   $28.00  
  Purchase #7 $62.90   5.710%   $66.4916   $66.49   $66.50   $66.50  
  7 purchase totals = $547.35       $586.0243   $586.02   $586.00   $586.00