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 $231.47   11.788%   $258.7557   $258.76   $258.75   $258.80  
  Purchase #2 $119.99   4.178%   $125.0032   $125.00   $125.00   $125.00  
  Purchase #3 $106.91   10.604%   $118.2467   $118.25   $118.25   $118.20  
  Purchase #4 $203.63   3.681%   $211.1256   $211.13   $211.15   $211.10  
  Purchase #5 $187.46   7.557%   $201.6264   $201.63   $201.65   $201.60  
  Purchase #6 $69.37   5.596%   $73.2519   $73.25   $73.25   $73.30  
  Purchase #7 $203.75   3.187%   $210.2435   $210.24   $210.25   $210.20  
  7 purchase totals = $1,122.58       $1,198.2530   $1,198.26   $1,198.30   $1,198.20