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 $95.85   3.229%   $98.945   $98.95   $98.95   $98.90  
  Purchase #2 $180.89   8.233%   $195.7827   $195.78   $195.80   $195.80  
  Purchase #3 $57.36   12.209%   $64.3631   $64.36   $64.35   $64.40  
  Purchase #4 $77.84   7.325%   $83.5418   $83.54   $83.55   $83.50  
  Purchase #5 $186.51   9.622%   $204.456   $204.46   $204.45   $204.50  
  Purchase #6 $103.84   9.788%   $114.0039   $114.00   $114.00   $114.00  
  Purchase #7 $177.48   11.145%   $197.2601   $197.26   $197.25   $197.30  
  7 purchase totals = $879.77       $958.3526   $958.35   $958.35   $958.40