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 $239.81   10.110%   $264.0548   $264.05   $264.05   $264.10  
  Purchase #2 $7.34   7.678%   $7.9036   $7.90   $7.90   $7.90  
  Purchase #3 $224.26   4.607%   $234.5917   $234.59   $234.60   $234.60  
  Purchase #4 $228.67   8.561%   $248.2464   $248.25   $248.25   $248.20  
  Purchase #5 $166.61   5.751%   $176.1917   $176.19   $176.20   $176.20  
  Purchase #6 $101.48   11.123%   $112.7676   $112.77   $112.75   $112.80  
  Purchase #7 $69.67   4.194%   $72.592   $72.59   $72.60   $72.60  
  7 purchase totals = $1,037.84       $1,116.3478   $1,116.34   $1,116.35   $1,116.40