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	$19.66	12.479%	$22.1134	$22.11	$22.10	$22.10
Purchase #2	$91.73	7.301%	$98.4272	$98.43	$98.45	$98.40
Purchase #3	$78.75	13.647%	$89.497	$89.50	$89.50	$89.50
Purchase #4	$205.42	12.372%	$230.8346	$230.83	$230.85	$230.80
Purchase #5	$183.48	4.138%	$191.0724	$191.07	$191.05	$191.10
Purchase #6	$137.43	4.781%	$144.0005	$144.00	$144.00	$144.00
Purchase #7	$11.78	4.470%	$12.3066	$12.31	$12.30	$12.30
7 purchase totals =	$728.25		$788.2517	$788.25	$788.25	$788.20