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 $65.63   13.164%   $74.2695   $74.27   $74.25   $74.30  
  Purchase #2 $152.30   9.303%   $166.4685   $166.47   $166.45   $166.50  
  Purchase #3 $60.55   3.338%   $62.5712   $62.57   $62.55   $62.60  
  Purchase #4 $157.55   3.204%   $162.5979   $162.60   $162.60   $162.60  
  Purchase #5 $26.61   5.582%   $28.0954   $28.10   $28.10   $28.10  
  Purchase #6 $177.57   5.202%   $186.8072   $186.81   $186.80   $186.80  
  Purchase #7 $92.81   9.471%   $101.6   $101.60   $101.60   $101.60  
  7 purchase totals = $733.02       $782.4097   $782.42   $782.35   $782.50