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 $23.98   3.677%   $24.8617   $24.86   $24.85   $24.90  
  Purchase #2 $190.72   5.393%   $201.0055   $201.01   $201.00   $201.00  
  Purchase #3 $169.81   12.838%   $191.6102   $191.61   $191.60   $191.60  
  Purchase #4 $46.80   12.830%   $52.8044   $52.80   $52.80   $52.80  
  Purchase #5 $215.35   12.339%   $241.922   $241.92   $241.90   $241.90  
  Purchase #6 $59.87   10.264%   $66.0151   $66.02   $66.00   $66.00  
  Purchase #7 $199.38   9.559%   $218.4387   $218.44   $218.45   $218.40  
  7 purchase totals = $905.91       $996.6576   $996.66   $996.60   $996.60