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 $237.83   6.273%   $252.7491   $252.75   $252.75   $252.70  
  Purchase #2 $232.92   4.543%   $243.5016   $243.50   $243.50   $243.50  
  Purchase #3 $215.34   12.474%   $242.2015   $242.20   $242.20   $242.20  
  Purchase #4 $21.35   11.275%   $23.7572   $23.76   $23.75   $23.80  
  Purchase #5 $161.72   6.722%   $172.5908   $172.59   $172.60   $172.60  
  Purchase #6 $14.37   4.465%   $15.0116   $15.01   $15.00   $15.00  
  Purchase #7 $244.49   5.718%   $258.4699   $258.47   $258.45   $258.50  
  7 purchase totals = $1,128.02       $1,208.2817   $1,208.28   $1,208.25   $1,208.30