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	$114.71	3.558%	$118.7914	$118.79	$118.80	$118.80
Purchase #2	$146.97	12.519%	$165.3692	$165.37	$165.35	$165.40
Purchase #3	$50.80	11.258%	$56.5191	$56.52	$56.50	$56.50
Purchase #4	$222.91	12.530%	$250.8406	$250.84	$250.85	$250.80
Purchase #5	$152.46	8.281%	$165.0852	$165.09	$165.10	$165.10
Purchase #6	$82.75	9.560%	$90.6609	$90.66	$90.65	$90.70
Purchase #7	$112.92	13.293%	$127.9305	$127.93	$127.95	$127.90
7 purchase totals =	$883.52		$975.1969	$975.20	$975.20	$975.20