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	$237.44	8.447%	$257.4966	$257.50	$257.50	$257.50
Purchase #2	$34.42	4.113%	$35.8357	$35.84	$35.85	$35.80
Purchase #3	$89.83	11.428%	$100.0958	$100.10	$100.10	$100.10
Purchase #4	$118.87	8.650%	$129.1523	$129.15	$129.15	$129.20
Purchase #5	$148.89	11.116%	$165.4406	$165.44	$165.45	$165.40
Purchase #6	$41.44	9.536%	$45.3917	$45.39	$45.40	$45.40
Purchase #7	$149.65	7.473%	$160.8333	$160.83	$160.85	$160.80
7 purchase totals =	$820.54		$894.2460	$894.25	$894.30	$894.20