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 $114.37   4.808%   $119.8689   $119.87   $119.85   $119.90  
  Purchase #2 $86.90   10.483%   $96.0097   $96.01   $96.00   $96.00  
  Purchase #3 $84.35   8.510%   $91.5282   $91.53   $91.55   $91.50  
  Purchase #4 $67.69   13.548%   $76.8606   $76.86   $76.85   $76.90  
  Purchase #5 $57.58   4.692%   $60.2817   $60.28   $60.30   $60.30  
  Purchase #6 $130.42   9.153%   $142.3573   $142.36   $142.35   $142.40  
  Purchase #7 $63.35   13.287%   $71.7673   $71.77   $71.75   $71.80  
  7 purchase totals = $604.66       $658.6737   $658.68   $658.65   $658.80