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 $247.35   11.705%   $276.3023   $276.30   $276.30   $276.30  
  Purchase #2 $215.51   11.223%   $239.6967   $239.70   $239.70   $239.70  
  Purchase #3 $80.31   11.120%   $89.2405   $89.24   $89.25   $89.20  
  Purchase #4 $222.54   8.253%   $240.9062   $240.91   $240.90   $240.90  
  Purchase #5 $147.27   4.780%   $154.3095   $154.31   $154.30   $154.30  
  Purchase #6 $192.99   12.464%   $217.0443   $217.04   $217.05   $217.00  
  Purchase #7 $90.39   7.380%   $97.0608   $97.06   $97.05   $97.10  
  7 purchase totals = $1,196.36       $1,314.5603   $1,314.56   $1,314.55   $1,314.50