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 $241.46   11.604%   $269.479   $269.48   $269.50   $269.50  
  Purchase #2 $124.87   5.303%   $131.4919   $131.49   $131.50   $131.50  
  Purchase #3 $211.66   13.510%   $240.2553   $240.26   $240.25   $240.30  
  Purchase #4 $230.26   5.476%   $242.869   $242.87   $242.85   $242.90  
  Purchase #5 $69.26   8.416%   $75.0889   $75.09   $75.10   $75.10  
  Purchase #6 $168.43   13.156%   $190.5887   $190.59   $190.60   $190.60  
  Purchase #7 $127.72   11.673%   $142.6288   $142.63   $142.65   $142.60  
  7 purchase totals = $1,173.66       $1,292.4016   $1,292.41   $1,292.45   $1,292.50