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	$42.66	7.488%	$45.8544	$45.85	$45.85	$45.90
Purchase #2	$241.25	12.380%	$271.1168	$271.12	$271.10	$271.10
Purchase #3	$172.43	3.860%	$179.0858	$179.09	$179.10	$179.10
Purchase #4	$102.69	4.836%	$107.6561	$107.66	$107.65	$107.70
Purchase #5	$16.74	10.113%	$18.4329	$18.43	$18.45	$18.40
Purchase #6	$96.49	7.424%	$103.6534	$103.65	$103.65	$103.70
Purchase #7	$89.84	5.184%	$94.4973	$94.50	$94.50	$94.50
7 purchase totals =	$762.10		$820.2967	$820.30	$820.30	$820.40