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 $248.67   6.393%   $264.5675   $264.57   $264.55   $264.60  
  Purchase #2 $131.63   11.157%   $146.316   $146.32   $146.30   $146.30  
  Purchase #3 $24.46   7.712%   $26.3464   $26.35   $26.35   $26.30  
  Purchase #4 $245.99   11.237%   $273.6319   $273.63   $273.65   $273.60  
  Purchase #5 $213.54   4.156%   $222.4147   $222.41   $222.40   $222.40  
  Purchase #6 $8.37   4.651%   $8.7593   $8.76   $8.75   $8.80  
  Purchase #7 $21.48   7.807%   $23.1569   $23.16   $23.15   $23.20  
  7 purchase totals = $894.14       $965.1927   $965.20   $965.15   $965.20