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 $226.37   9.708%   $248.346   $248.35   $248.35   $248.30  
  Purchase #2 $167.66   4.157%   $174.6296   $174.63   $174.65   $174.60  
  Purchase #3 $47.46   6.373%   $50.4846   $50.48   $50.50   $50.50  
  Purchase #4 $125.34   4.347%   $130.7885   $130.79   $130.80   $130.80  
  Purchase #5 $195.48   11.710%   $218.3707   $218.37   $218.35   $218.40  
  Purchase #6 $226.74   9.385%   $248.0195   $248.02   $248.00   $248.00  
  Purchase #7 $147.28   13.128%   $166.6149   $166.61   $166.60   $166.60  
  7 purchase totals = $1,136.33       $1,237.2538   $1,237.25   $1,237.25   $1,237.20