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	$80.83	12.760%	$91.1439	$91.14	$91.15	$91.10
Purchase #2	$28.80	11.525%	$32.1192	$32.12	$32.10	$32.10
Purchase #3	$165.40	11.582%	$184.5566	$184.56	$184.55	$184.60
Purchase #4	$110.91	4.749%	$116.1771	$116.18	$116.20	$116.20
Purchase #5	$125.27	13.719%	$142.4558	$142.46	$142.45	$142.50
Purchase #6	$49.54	4.200%	$51.6207	$51.62	$51.60	$51.60
Purchase #7	$250.41	10.202%	$275.9568	$275.96	$275.95	$276.00
7 purchase totals =	$811.16		$894.0301	$894.04	$894.00	$894.10