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 $247.37   11.451%   $275.6963   $275.70   $275.70   $275.70  
  Purchase #2 $182.83   5.257%   $192.4414   $192.44   $192.45   $192.40  
  Purchase #3 $227.59   4.240%   $237.2398   $237.24   $237.25   $237.20  
  Purchase #4 $171.32   7.602%   $184.3437   $184.34   $184.35   $184.30  
  Purchase #5 $49.54   8.185%   $53.5948   $53.59   $53.60   $53.60  
  Purchase #6 $144.79   8.432%   $156.9987   $157.00   $157.00   $157.00  
  Purchase #7 $185.43   8.536%   $201.2583   $201.26   $201.25   $201.30  
  7 purchase totals = $1,208.87       $1,301.5730   $1,301.57   $1,301.60   $1,301.50