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 $231.43   13.528%   $262.7379   $262.74   $262.75   $262.70  
  Purchase #2 $104.70   4.843%   $109.7706   $109.77   $109.75   $109.80  
  Purchase #3 $113.57   7.357%   $121.9253   $121.93   $121.95   $121.90  
  Purchase #4 $167.73   11.670%   $187.3041   $187.30   $187.30   $187.30  
  Purchase #5 $74.44   11.256%   $82.819   $82.82   $82.80   $82.80  
  Purchase #6 $208.81   4.404%   $218.006   $218.01   $218.00   $218.00  
  Purchase #7 $119.69   11.534%   $133.495   $133.50   $133.50   $133.50  
  7 purchase totals = $1,020.37       $1,116.0579   $1,116.07   $1,116.05   $1,116.00