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 $244.65   7.212%   $262.2942   $262.29   $262.30   $262.30  
  Purchase #2 $130.58   3.685%   $135.3919   $135.39   $135.40   $135.40  
  Purchase #3 $113.25   4.672%   $118.541   $118.54   $118.55   $118.50  
  Purchase #4 $210.33   7.773%   $226.679   $226.68   $226.70   $226.70  
  Purchase #5 $169.30   13.469%   $192.103   $192.10   $192.10   $192.10  
  Purchase #6 $152.31   3.553%   $157.7216   $157.72   $157.70   $157.70  
  Purchase #7 $214.45   10.155%   $236.2274   $236.23   $236.25   $236.20  
  7 purchase totals = $1,234.87       $1,328.9581   $1,328.95   $1,329.00   $1,328.90