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 $24.58   3.124%   $25.3479   $25.35   $25.35   $25.30  
  Purchase #2 $185.48   12.543%   $208.7448   $208.74   $208.75   $208.70  
  Purchase #3 $165.46   7.448%   $177.7835   $177.78   $177.80   $177.80  
  Purchase #4 $107.94   4.583%   $112.8869   $112.89   $112.90   $112.90  
  Purchase #5 $19.51   5.155%   $20.5157   $20.52   $20.50   $20.50  
  Purchase #6 $206.80   12.426%   $232.497   $232.50   $232.50   $232.50  
  Purchase #7 $84.26   11.749%   $94.1597   $94.16   $94.15   $94.20  
  7 purchase totals = $794.03       $871.9355   $871.94   $871.95   $871.90