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 $212.25   13.526%   $240.9589   $240.96   $240.95   $241.00  
  Purchase #2 $247.55   6.223%   $262.955   $262.96   $262.95   $263.00  
  Purchase #3 $244.93   10.302%   $270.1627   $270.16   $270.15   $270.20  
  Purchase #4 $22.26   12.463%   $25.0343   $25.03   $25.05   $25.00  
  Purchase #5 $165.53   13.849%   $188.4542   $188.45   $188.45   $188.50  
  Purchase #6 $250.59   7.181%   $268.5849   $268.58   $268.60   $268.60  
  Purchase #7 $176.57   9.112%   $192.6591   $192.66   $192.65   $192.70  
  7 purchase totals = $1,319.68       $1,448.8091   $1,448.80   $1,448.80   $1,449.00