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	$117.59	10.436%	$129.8617	$129.86	$129.85	$129.90
Purchase #2	$90.28	11.135%	$100.3327	$100.33	$100.35	$100.30
Purchase #3	$131.31	9.721%	$144.0746	$144.07	$144.05	$144.10
Purchase #4	$94.74	11.252%	$105.4001	$105.40	$105.40	$105.40
Purchase #5	$204.34	3.104%	$210.6827	$210.68	$210.70	$210.70
Purchase #6	$98.50	6.791%	$105.1891	$105.19	$105.20	$105.20
Purchase #7	$48.53	9.307%	$53.0467	$53.05	$53.05	$53.00
7 purchase totals =	$785.29		$848.5876	$848.58	$848.60	$848.60