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 $246.63   8.493%   $267.5763   $267.58   $267.60   $267.60  
  Purchase #2 $127.40   5.311%   $134.1662   $134.17   $134.15   $134.20  
  Purchase #3 $233.96   8.501%   $253.8489   $253.85   $253.85   $253.80  
  Purchase #4 $164.96   9.214%   $180.1594   $180.16   $180.15   $180.20  
  Purchase #5 $95.42   3.753%   $99.0011   $99.00   $99.00   $99.00  
  Purchase #6 $121.57   9.775%   $133.4535   $133.45   $133.45   $133.50  
  Purchase #7 $186.54   4.851%   $195.5891   $195.59   $195.60   $195.60  
  7 purchase totals = $1,176.48       $1,263.7945   $1,263.80   $1,263.80   $1,263.90