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   6.863%   $255.83   $255.83   $255.85   $255.80  
  Purchase #2 $160.97   5.146%   $169.2535   $169.25   $169.25   $169.30  
  Purchase #3 $57.33   7.222%   $61.4704   $61.47   $61.45   $61.50  
  Purchase #4 $239.63   7.769%   $258.2469   $258.25   $258.25   $258.20  
  Purchase #5 $118.40   13.243%   $134.0797   $134.08   $134.10   $134.10  
  Purchase #6 $124.32   10.790%   $137.7341   $137.73   $137.75   $137.70  
  Purchase #7 $14.47   10.497%   $15.9889   $15.99   $16.00   $16.00  
  7 purchase totals = $954.52       $1,032.6035   $1,032.60   $1,032.65   $1,032.60