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	$144.40	11.762%	$161.3843	$161.38	$161.40	$161.40
Purchase #2	$30.44	9.388%	$33.2977	$33.30	$33.30	$33.30
Purchase #3	$21.61	3.786%	$22.4282	$22.43	$22.45	$22.40
Purchase #4	$216.75	7.648%	$233.327	$233.33	$233.35	$233.30
Purchase #5	$196.28	13.615%	$223.0035	$223.00	$223.00	$223.00
Purchase #6	$103.33	10.787%	$114.4762	$114.48	$114.50	$114.50
Purchase #7	$96.32	4.442%	$100.5985	$100.60	$100.60	$100.60
7 purchase totals =	$809.13		$888.5154	$888.52	$888.60	$888.50