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 $208.65   7.711%   $224.739   $224.74   $224.75   $224.70  
  Purchase #2 $14.27   5.450%   $15.0477   $15.05   $15.05   $15.00  
  Purchase #3 $23.63   3.258%   $24.3999   $24.40   $24.40   $24.40  
  Purchase #4 $70.88   9.327%   $77.491   $77.49   $77.50   $77.50  
  Purchase #5 $238.58   9.289%   $260.7417   $260.74   $260.75   $260.70  
  Purchase #6 $32.62   8.862%   $35.5108   $35.51   $35.50   $35.50  
  Purchase #7 $193.67   5.241%   $203.8202   $203.82   $203.80   $203.80  
  7 purchase totals = $782.30       $841.7503   $841.75   $841.75   $841.60