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 $245.86   3.848%   $255.3207   $255.32   $255.30   $255.30  
  Purchase #2 $103.65   13.591%   $117.7371   $117.74   $117.75   $117.70  
  Purchase #3 $98.77   13.138%   $111.7464   $111.75   $111.75   $111.70  
  Purchase #4 $197.29   4.153%   $205.4835   $205.48   $205.50   $205.50  
  Purchase #5 $64.87   4.863%   $68.0246   $68.02   $68.00   $68.00  
  Purchase #6 $119.84   6.318%   $127.4115   $127.41   $127.40   $127.40  
  Purchase #7 $136.89   7.382%   $146.9952   $147.00   $147.00   $147.00  
  7 purchase totals = $967.17       $1,032.7190   $1,032.72   $1,032.70   $1,032.60