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 $116.38   10.698%   $128.8303   $128.83   $128.85   $128.80  
  Purchase #2 $247.95   4.796%   $259.8417   $259.84   $259.85   $259.80  
  Purchase #3 $78.56   4.202%   $81.8611   $81.86   $81.85   $81.90  
  Purchase #4 $216.79   4.107%   $225.6936   $225.69   $225.70   $225.70  
  Purchase #5 $73.63   3.130%   $75.9346   $75.93   $75.95   $75.90  
  Purchase #6 $18.43   3.322%   $19.0422   $19.04   $19.05   $19.00  
  Purchase #7 $167.77   5.385%   $176.8044   $176.80   $176.80   $176.80  
  7 purchase totals = $919.51       $968.0079   $967.99   $968.05   $967.90