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 $89.42   10.209%   $98.5489   $98.55   $98.55   $98.50  
  Purchase #2 $241.96   11.312%   $269.3305   $269.33   $269.35   $269.30  
  Purchase #3 $233.95   5.700%   $247.2852   $247.29   $247.30   $247.30  
  Purchase #4 $226.76   4.847%   $237.7511   $237.75   $237.75   $237.80  
  Purchase #5 $23.94   4.455%   $25.0065   $25.01   $25.00   $25.00  
  Purchase #6 $242.99   11.124%   $270.0202   $270.02   $270.00   $270.00  
  Purchase #7 $125.65   11.519%   $140.1236   $140.12   $140.10   $140.10  
  7 purchase totals = $1,184.67       $1,288.0660   $1,288.07   $1,288.05   $1,288.00