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	$27.91	9.863%	$30.6628	$30.66	$30.65	$30.70
Purchase #2	$69.47	6.526%	$74.0036	$74.00	$74.00	$74.00
Purchase #3	$225.32	13.500%	$255.7382	$255.74	$255.75	$255.70
Purchase #4	$102.42	11.799%	$114.5045	$114.50	$114.50	$114.50
Purchase #5	$244.74	11.248%	$272.2684	$272.27	$272.25	$272.30
Purchase #6	$227.96	11.587%	$254.3737	$254.37	$254.35	$254.40
Purchase #7	$106.66	4.461%	$111.4181	$111.42	$111.40	$111.40
7 purchase totals =	$1,004.48		$1,112.9693	$1,112.96	$1,112.90	$1,113.00