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	$37.88	11.334%	$42.1733	$42.17	$42.15	$42.20
Purchase #2	$227.49	3.766%	$236.0573	$236.06	$236.05	$236.10
Purchase #3	$95.74	4.759%	$100.2963	$100.30	$100.30	$100.30
Purchase #4	$143.62	7.734%	$154.7276	$154.73	$154.75	$154.70
Purchase #5	$105.54	3.550%	$109.2867	$109.29	$109.30	$109.30
Purchase #6	$197.76	5.452%	$208.5419	$208.54	$208.55	$208.50
Purchase #7	$33.44	9.225%	$36.5248	$36.52	$36.50	$36.50
7 purchase totals =	$841.47		$887.6079	$887.61	$887.60	$887.60