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 $207.77   6.802%   $221.9025   $221.90   $221.90   $221.90  
  Purchase #2 $29.95   7.792%   $32.2837   $32.28   $32.30   $32.30  
  Purchase #3 $105.62   6.283%   $112.2561   $112.26   $112.25   $112.30  
  Purchase #4 $230.65   10.123%   $253.9987   $254.00   $254.00   $254.00  
  Purchase #5 $180.44   4.401%   $188.3812   $188.38   $188.40   $188.40  
  Purchase #6 $197.46   9.262%   $215.7487   $215.75   $215.75   $215.70  
  Purchase #7 $172.38   11.404%   $192.0382   $192.04   $192.05   $192.00  
  7 purchase totals = $1,124.27       $1,216.6091   $1,216.61   $1,216.65   $1,216.60