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 $66.90   10.430%   $73.8777   $73.88   $73.90   $73.90  
  Purchase #2 $95.25   7.680%   $102.5652   $102.57   $102.55   $102.60  
  Purchase #3 $198.78   7.789%   $214.263   $214.26   $214.25   $214.30  
  Purchase #4 $243.38   4.675%   $254.758   $254.76   $254.75   $254.80  
  Purchase #5 $141.86   13.699%   $161.2934   $161.29   $161.30   $161.30  
  Purchase #6 $36.53   7.688%   $39.3384   $39.34   $39.35   $39.30  
  Purchase #7 $103.36   11.133%   $114.8671   $114.87   $114.85   $114.90  
  7 purchase totals = $886.06       $960.9628   $960.97   $960.95   $961.10