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	$183.38	3.670%	$190.11	$190.11	$190.10	$190.10
Purchase #2	$136.38	7.412%	$146.4885	$146.49	$146.50	$146.50
Purchase #3	$156.66	13.447%	$177.7261	$177.73	$177.75	$177.70
Purchase #4	$111.35	11.308%	$123.9415	$123.94	$123.95	$123.90
Purchase #5	$131.31	12.178%	$147.3009	$147.30	$147.30	$147.30
Purchase #6	$241.27	9.307%	$263.725	$263.73	$263.75	$263.70
Purchase #7	$96.63	9.456%	$105.7673	$105.77	$105.75	$105.80
7 purchase totals =	$1,056.98		$1,155.0593	$1,155.07	$1,155.10	$1,155.00