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 $40.54   8.102%   $43.8246   $43.82   $43.80   $43.80  
  Purchase #2 $224.65   4.466%   $234.6829   $234.68   $234.70   $234.70  
  Purchase #3 $237.75   12.190%   $266.7317   $266.73   $266.75   $266.70  
  Purchase #4 $96.64   4.653%   $101.1367   $101.14   $101.15   $101.10  
  Purchase #5 $107.40   8.401%   $116.4227   $116.42   $116.40   $116.40  
  Purchase #6 $10.25   13.173%   $11.6002   $11.60   $11.60   $11.60  
  Purchase #7 $16.83   5.302%   $17.7223   $17.72   $17.70   $17.70  
  7 purchase totals = $734.06       $792.1211   $792.11   $792.10   $792.00