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	$70.90	5.240%	$74.6152	$74.62	$74.60	$74.60
Purchase #2	$168.39	10.282%	$185.7039	$185.70	$185.70	$185.70
Purchase #3	$145.77	4.639%	$152.5323	$152.53	$152.55	$152.50
Purchase #4	$161.43	6.721%	$172.2797	$172.28	$172.30	$172.30
Purchase #5	$106.26	4.385%	$110.9195	$110.92	$110.90	$110.90
Purchase #6	$190.78	10.724%	$211.2392	$211.24	$211.25	$211.20
Purchase #7	$65.26	10.154%	$71.8865	$71.89	$71.90	$71.90
7 purchase totals =	$908.79		$979.1763	$979.18	$979.20	$979.10