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	$194.35	8.443%	$210.759	$210.76	$210.75	$210.80
Purchase #2	$40.49	11.176%	$45.0152	$45.02	$45.00	$45.00
Purchase #3	$148.52	13.563%	$168.6638	$168.66	$168.65	$168.70
Purchase #4	$114.71	11.148%	$127.4979	$127.50	$127.50	$127.50
Purchase #5	$58.81	9.352%	$64.3099	$64.31	$64.30	$64.30
Purchase #6	$129.97	5.363%	$136.9403	$136.94	$136.95	$136.90
Purchase #7	$117.71	10.773%	$130.3909	$130.39	$130.40	$130.40
7 purchase totals =	$804.56		$883.5770	$883.58	$883.55	$883.60