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 $59.36   8.865%   $64.6223   $64.62   $64.60   $64.60  
  Purchase #2 $222.91   7.532%   $239.6996   $239.70   $239.70   $239.70  
  Purchase #3 $33.28   3.777%   $34.537   $34.54   $34.55   $34.50  
  Purchase #4 $184.71   4.404%   $192.8446   $192.84   $192.85   $192.80  
  Purchase #5 $140.34   3.197%   $144.8267   $144.83   $144.85   $144.80  
  Purchase #6 $42.73   10.593%   $47.2564   $47.26   $47.25   $47.30  
  Purchase #7 $28.40   11.372%   $31.6296   $31.63   $31.65   $31.60  
  7 purchase totals = $711.73       $755.4162   $755.42   $755.45   $755.30