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	$133.76	7.574%	$143.891	$143.89	$143.90	$143.90
Purchase #2	$99.58	9.566%	$109.1058	$109.11	$109.10	$109.10
Purchase #3	$101.29	5.704%	$107.0676	$107.07	$107.05	$107.10
Purchase #4	$176.68	6.415%	$188.014	$188.01	$188.00	$188.00
Purchase #5	$248.97	12.111%	$279.1228	$279.12	$279.10	$279.10
Purchase #6	$233.82	3.310%	$241.5594	$241.56	$241.55	$241.60
Purchase #7	$36.76	11.102%	$40.8411	$40.84	$40.85	$40.80
7 purchase totals =	$1,030.86		$1,109.6017	$1,109.60	$1,109.55	$1,109.60