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 $55.29   8.116%   $59.7773   $59.78   $59.80   $59.80  
  Purchase #2 $114.96   6.402%   $122.3197   $122.32   $122.30   $122.30  
  Purchase #3 $168.41   4.531%   $176.0407   $176.04   $176.05   $176.00  
  Purchase #4 $248.82   5.544%   $262.6146   $262.61   $262.60   $262.60  
  Purchase #5 $5.75   11.520%   $6.4124   $6.41   $6.40   $6.40  
  Purchase #6 $105.65   9.771%   $115.9731   $115.97   $115.95   $116.00  
  Purchase #7 $7.32   9.130%   $7.9883   $7.99   $8.00   $8.00  
  7 purchase totals = $706.20       $751.1261   $751.12   $751.10   $751.10