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 $213.43   11.202%   $237.3384   $237.34   $237.35   $237.30  
  Purchase #2 $228.72   4.132%   $238.1707   $238.17   $238.15   $238.20  
  Purchase #3 $211.83   12.829%   $239.0057   $239.01   $239.00   $239.00  
  Purchase #4 $175.46   10.549%   $193.9693   $193.97   $193.95   $194.00  
  Purchase #5 $168.57   8.267%   $182.5057   $182.51   $182.50   $182.50  
  Purchase #6 $151.75   3.855%   $157.6   $157.60   $157.60   $157.60  
  Purchase #7 $247.45   9.493%   $270.9404   $270.94   $270.95   $270.90  
  7 purchase totals = $1,397.21       $1,519.5302   $1,519.54   $1,519.50   $1,519.50