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 $59.83   3.472%   $61.9073   $61.91   $61.90   $61.90  
  Purchase #2 $35.81   11.737%   $40.013   $40.01   $40.00   $40.00  
  Purchase #3 $157.48   10.639%   $174.2343   $174.23   $174.25   $174.20  
  Purchase #4 $114.88   4.714%   $120.2954   $120.30   $120.30   $120.30  
  Purchase #5 $119.38   13.814%   $135.8712   $135.87   $135.85   $135.90  
  Purchase #6 $40.26   9.715%   $44.1713   $44.17   $44.15   $44.20  
  Purchase #7 $150.26   11.480%   $167.5098   $167.51   $167.50   $167.50  
  7 purchase totals = $677.90       $744.0023   $744.00   $743.95   $744.00