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	$143.72	12.287%	$161.3789	$161.38	$161.40	$161.40
Purchase #2	$141.94	5.617%	$149.9128	$149.91	$149.90	$149.90
Purchase #3	$84.95	5.765%	$89.8474	$89.85	$89.85	$89.80
Purchase #4	$165.57	8.309%	$179.3272	$179.33	$179.35	$179.30
Purchase #5	$74.94	7.120%	$80.2757	$80.28	$80.30	$80.30
Purchase #6	$183.58	11.697%	$205.0534	$205.05	$205.05	$205.10
Purchase #7	$62.88	7.765%	$67.7626	$67.76	$67.75	$67.80
7 purchase totals =	$857.58		$933.5580	$933.56	$933.60	$933.60