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 $216.92   13.555%   $246.3235   $246.32   $246.30   $246.30  
  Purchase #2 $22.58   9.452%   $24.7143   $24.71   $24.70   $24.70  
  Purchase #3 $229.36   3.176%   $236.6445   $236.64   $236.65   $236.60  
  Purchase #4 $10.35   9.826%   $11.367   $11.37   $11.35   $11.40  
  Purchase #5 $35.52   5.144%   $37.3471   $37.35   $37.35   $37.30  
  Purchase #6 $136.57   12.809%   $154.0633   $154.06   $154.05   $154.10  
  Purchase #7 $73.93   3.497%   $76.5153   $76.52   $76.50   $76.50  
  7 purchase totals = $725.23       $786.9750   $786.97   $786.90   $786.90