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 $23.97   10.827%   $26.5652   $26.57   $26.55   $26.60  
  Purchase #2 $86.28   12.333%   $96.9209   $96.92   $96.90   $96.90  
  Purchase #3 $248.38   11.521%   $276.9959   $277.00   $277.00   $277.00  
  Purchase #4 $148.65   8.777%   $161.697   $161.70   $161.70   $161.70  
  Purchase #5 $71.88   4.320%   $74.9852   $74.99   $75.00   $75.00  
  Purchase #6 $19.95   5.225%   $20.9924   $20.99   $21.00   $21.00  
  Purchase #7 $62.73   10.512%   $69.3242   $69.32   $69.30   $69.30  
  7 purchase totals = $661.84       $727.4808   $727.49   $727.45   $727.50