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 $215.77   11.369%   $240.3009   $240.30   $240.30   $240.30  
  Purchase #2 $216.58   10.750%   $239.8624   $239.86   $239.85   $239.90  
  Purchase #3 $112.86   13.230%   $127.7914   $127.79   $127.80   $127.80  
  Purchase #4 $176.95   12.849%   $199.6863   $199.69   $199.70   $199.70  
  Purchase #5 $193.67   7.222%   $207.6568   $207.66   $207.65   $207.70  
  Purchase #6 $135.67   8.500%   $147.202   $147.20   $147.20   $147.20  
  Purchase #7 $59.64   4.293%   $62.2003   $62.20   $62.20   $62.20  
  7 purchase totals = $1,111.14       $1,224.7001   $1,224.70   $1,224.70   $1,224.80