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 $104.73   11.437%   $116.708   $116.71   $116.70   $116.70  
  Purchase #2 $200.44   9.234%   $218.9486   $218.95   $218.95   $218.90  
  Purchase #3 $192.54   9.482%   $210.7966   $210.80   $210.80   $210.80  
  Purchase #4 $51.46   4.455%   $53.7525   $53.75   $53.75   $53.80  
  Purchase #5 $93.86   11.396%   $104.5563   $104.56   $104.55   $104.60  
  Purchase #6 $45.56   3.571%   $47.1869   $47.19   $47.20   $47.20  
  Purchase #7 $246.78   10.116%   $271.7443   $271.74   $271.75   $271.70  
  7 purchase totals = $935.37       $1,023.6932   $1,023.70   $1,023.70   $1,023.70