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	$38.48	6.335%	$40.9177	$40.92	$40.90	$40.90
Purchase #2	$117.44	3.740%	$121.8323	$121.83	$121.85	$121.80
Purchase #3	$141.72	4.793%	$148.5126	$148.51	$148.50	$148.50
Purchase #4	$166.34	3.496%	$172.1552	$172.16	$172.15	$172.20
Purchase #5	$30.88	3.510%	$31.9639	$31.96	$31.95	$32.00
Purchase #6	$175.54	9.139%	$191.5826	$191.58	$191.60	$191.60
Purchase #7	$115.77	11.525%	$129.1125	$129.11	$129.10	$129.10
7 purchase totals =	$786.17		$836.0768	$836.07	$836.05	$836.10