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	$26.69	11.850%	$29.8528	$29.85	$29.85	$29.90
Purchase #2	$244.83	9.748%	$268.696	$268.70	$268.70	$268.70
Purchase #3	$184.33	8.565%	$200.1179	$200.12	$200.10	$200.10
Purchase #4	$134.47	10.417%	$148.4777	$148.48	$148.50	$148.50
Purchase #5	$175.92	11.472%	$196.1015	$196.10	$196.10	$196.10
Purchase #6	$164.87	3.193%	$170.1343	$170.13	$170.15	$170.10
Purchase #7	$172.94	7.457%	$185.8361	$185.84	$185.85	$185.80
7 purchase totals =	$1,104.05		$1,199.2163	$1,199.22	$1,199.25	$1,199.20