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 $53.65   13.726%   $61.014   $61.01   $61.00   $61.00  
  Purchase #2 $37.55   11.639%   $41.9204   $41.92   $41.90   $41.90  
  Purchase #3 $242.47   12.445%   $272.6454   $272.65   $272.65   $272.60  
  Purchase #4 $183.63   12.708%   $206.9657   $206.97   $206.95   $207.00  
  Purchase #5 $207.92   10.859%   $230.498   $230.50   $230.50   $230.50  
  Purchase #6 $244.35   9.426%   $267.3824   $267.38   $267.40   $267.40  
  Purchase #7 $193.30   11.699%   $215.9142   $215.91   $215.90   $215.90  
  7 purchase totals = $1,162.87       $1,296.3401   $1,296.34   $1,296.30   $1,296.30