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 $211.34   5.674%   $223.3314   $223.33   $223.35   $223.30  
  Purchase #2 $40.71   5.635%   $43.004   $43.00   $43.00   $43.00  
  Purchase #3 $56.60   3.548%   $58.6082   $58.61   $58.60   $58.60  
  Purchase #4 $121.93   13.237%   $138.0699   $138.07   $138.05   $138.10  
  Purchase #5 $6.68   8.193%   $7.2273   $7.23   $7.25   $7.20  
  Purchase #6 $95.51   6.699%   $101.9082   $101.91   $101.90   $101.90  
  Purchase #7 $249.81   5.827%   $264.3664   $264.37   $264.35   $264.40  
  7 purchase totals = $782.58       $836.5154   $836.52   $836.50   $836.50