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 $52.98   12.790%   $59.7561   $59.76   $59.75   $59.80  
  Purchase #2 $248.47   7.645%   $267.4655   $267.47   $267.45   $267.50  
  Purchase #3 $238.53   3.291%   $246.38   $246.38   $246.40   $246.40  
  Purchase #4 $209.97   5.358%   $221.2202   $221.22   $221.20   $221.20  
  Purchase #5 $106.87   6.825%   $114.1639   $114.16   $114.15   $114.20  
  Purchase #6 $21.69   10.394%   $23.9445   $23.94   $23.95   $23.90  
  Purchase #7 $93.53   3.549%   $96.8494   $96.85   $96.85   $96.80  
  7 purchase totals = $972.04       $1,029.7796   $1,029.78   $1,029.75   $1,029.80