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 $111.67   10.611%   $123.5193   $123.52   $123.50   $123.50  
  Purchase #2 $156.41   13.385%   $177.3455   $177.35   $177.35   $177.30  
  Purchase #3 $17.42   5.747%   $18.4211   $18.42   $18.40   $18.40  
  Purchase #4 $51.39   11.392%   $57.2443   $57.24   $57.25   $57.20  
  Purchase #5 $163.78   8.613%   $177.8864   $177.89   $177.90   $177.90  
  Purchase #6 $207.79   13.594%   $236.037   $236.04   $236.05   $236.00  
  Purchase #7 $63.87   11.844%   $71.4348   $71.43   $71.45   $71.40  
  7 purchase totals = $772.33       $861.8884   $861.89   $861.90   $861.70