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 $56.66   5.836%   $59.9667   $59.97   $59.95   $60.00  
  Purchase #2 $44.43   7.285%   $47.6667   $47.67   $47.65   $47.70  
  Purchase #3 $176.59   13.772%   $200.91   $200.91   $200.90   $200.90  
  Purchase #4 $240.35   7.190%   $257.6312   $257.63   $257.65   $257.60  
  Purchase #5 $56.62   11.230%   $62.9784   $62.98   $63.00   $63.00  
  Purchase #6 $19.39   8.341%   $21.0073   $21.01   $21.00   $21.00  
  Purchase #7 $76.94   7.645%   $82.8221   $82.82   $82.80   $82.80  
  7 purchase totals = $670.98       $732.9824   $732.99   $732.95   $733.00