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 $60.97   8.131%   $65.9275   $65.93   $65.95   $65.90  
  Purchase #2 $13.91   10.692%   $15.3973   $15.40   $15.40   $15.40  
  Purchase #3 $32.47   6.610%   $34.6163   $34.62   $34.60   $34.60  
  Purchase #4 $218.87   12.384%   $245.9749   $245.97   $245.95   $246.00  
  Purchase #5 $73.60   8.559%   $79.8994   $79.90   $79.90   $79.90  
  Purchase #6 $159.66   9.319%   $174.5387   $174.54   $174.55   $174.50  
  Purchase #7 $149.27   5.330%   $157.2261   $157.23   $157.25   $157.20  
  7 purchase totals = $708.75       $773.5802   $773.59   $773.60   $773.50