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	$230.53	3.382%	$238.3265	$238.33	$238.35	$238.30
Purchase #2	$30.44	3.656%	$31.5529	$31.55	$31.55	$31.60
Purchase #3	$17.49	6.169%	$18.569	$18.57	$18.55	$18.60
Purchase #4	$33.33	5.658%	$35.2158	$35.22	$35.20	$35.20
Purchase #5	$143.64	11.335%	$159.9216	$159.92	$159.90	$159.90
Purchase #6	$104.26	10.586%	$115.297	$115.30	$115.30	$115.30
Purchase #7	$105.38	5.807%	$111.4994	$111.50	$111.50	$111.50
7 purchase totals =	$665.07		$710.3822	$710.39	$710.35	$710.40