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 $69.26   8.212%   $74.9476   $74.95   $74.95   $74.90  
  Purchase #2 $177.72   3.473%   $183.8922   $183.89   $183.90   $183.90  
  Purchase #3 $101.57   10.530%   $112.2653   $112.27   $112.25   $112.30  
  Purchase #4 $175.98   13.615%   $199.9397   $199.94   $199.95   $199.90  
  Purchase #5 $26.89   12.425%   $30.2311   $30.23   $30.25   $30.20  
  Purchase #6 $86.81   7.602%   $93.4093   $93.41   $93.40   $93.40  
  Purchase #7 $169.46   5.784%   $179.2616   $179.26   $179.25   $179.30  
  7 purchase totals = $807.69       $873.9468   $873.95   $873.95   $873.90