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	$18.25	11.872%	$20.4166	$20.42	$20.40	$20.40
Purchase #2	$245.92	3.531%	$254.6034	$254.60	$254.60	$254.60
Purchase #3	$91.96	13.307%	$104.1971	$104.20	$104.20	$104.20
Purchase #4	$10.91	12.426%	$12.2657	$12.27	$12.25	$12.30
Purchase #5	$243.50	3.247%	$251.4064	$251.41	$251.40	$251.40
Purchase #6	$157.64	9.367%	$172.4061	$172.41	$172.40	$172.40
Purchase #7	$232.71	4.435%	$243.0307	$243.03	$243.05	$243.00
7 purchase totals =	$1,000.89		$1,058.3260	$1,058.34	$1,058.30	$1,058.30