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 $124.35   9.120%   $135.6907   $135.69   $135.70   $135.70  
  Purchase #2 $145.63   8.186%   $157.5513   $157.55   $157.55   $157.60  
  Purchase #3 $91.91   8.297%   $99.5358   $99.54   $99.55   $99.50  
  Purchase #4 $231.68   7.247%   $248.4698   $248.47   $248.45   $248.50  
  Purchase #5 $37.85   8.387%   $41.0245   $41.02   $41.00   $41.00  
  Purchase #6 $75.68   7.425%   $81.2992   $81.30   $81.30   $81.30  
  Purchase #7 $249.41   5.276%   $262.5689   $262.57   $262.55   $262.60  
  7 purchase totals = $956.51       $1,026.1402   $1,026.14   $1,026.10   $1,026.20