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 $196.38   13.659%   $223.2035   $223.20   $223.20   $223.20  
  Purchase #2 $168.70   4.497%   $176.2864   $176.29   $176.30   $176.30  
  Purchase #3 $86.60   9.194%   $94.562   $94.56   $94.55   $94.60  
  Purchase #4 $210.45   13.860%   $239.6184   $239.62   $239.60   $239.60  
  Purchase #5 $99.80   7.518%   $107.303   $107.30   $107.30   $107.30  
  Purchase #6 $114.31   11.751%   $127.7426   $127.74   $127.75   $127.70  
  Purchase #7 $114.45   3.634%   $118.6091   $118.61   $118.60   $118.60  
  7 purchase totals = $990.69       $1,087.3250   $1,087.32   $1,087.30   $1,087.30