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	$211.83	5.455%	$223.3853	$223.39	$223.40	$223.40
Purchase #2	$107.55	6.200%	$114.2181	$114.22	$114.20	$114.20
Purchase #3	$37.43	7.800%	$40.3495	$40.35	$40.35	$40.30
Purchase #4	$244.57	12.407%	$274.9138	$274.91	$274.90	$274.90
Purchase #5	$6.36	3.605%	$6.5893	$6.59	$6.60	$6.60
Purchase #6	$186.59	4.105%	$194.2495	$194.25	$194.25	$194.20
Purchase #7	$52.95	6.827%	$56.5649	$56.56	$56.55	$56.60
7 purchase totals =	$847.28		$910.2704	$910.27	$910.25	$910.20