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	$95.56	4.656%	$100.0093	$100.01	$100.00	$100.00
Purchase #2	$166.40	13.479%	$188.8291	$188.83	$188.85	$188.80
Purchase #3	$171.35	5.104%	$180.0957	$180.10	$180.10	$180.10
Purchase #4	$62.73	7.373%	$67.3551	$67.36	$67.35	$67.40
Purchase #5	$141.33	3.515%	$146.2977	$146.30	$146.30	$146.30
Purchase #6	$129.89	11.379%	$144.6702	$144.67	$144.65	$144.70
Purchase #7	$214.52	4.569%	$224.3214	$224.32	$224.30	$224.30
7 purchase totals =	$981.78		$1,051.5785	$1,051.59	$1,051.55	$1,051.60