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 $239.40   11.538%   $267.022   $267.02   $267.00   $267.00  
  Purchase #2 $213.95   6.563%   $227.9915   $227.99   $228.00   $228.00  
  Purchase #3 $231.26   10.450%   $255.4267   $255.43   $255.45   $255.40  
  Purchase #4 $163.69   11.856%   $183.0971   $183.10   $183.10   $183.10  
  Purchase #5 $19.94   13.147%   $22.5615   $22.56   $22.55   $22.60  
  Purchase #6 $212.26   9.539%   $232.5075   $232.51   $232.50   $232.50  
  Purchase #7 $135.62   3.299%   $140.0941   $140.09   $140.10   $140.10  
  7 purchase totals = $1,216.12       $1,328.7004   $1,328.70   $1,328.70   $1,328.70