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	$170.58	8.847%	$185.6712	$185.67	$185.65	$185.70
Purchase #2	$177.74	7.119%	$190.3933	$190.39	$190.40	$190.40
Purchase #3	$163.56	5.663%	$172.8224	$172.82	$172.80	$172.80
Purchase #4	$8.92	13.409%	$10.1161	$10.12	$10.10	$10.10
Purchase #5	$80.75	10.256%	$89.0317	$89.03	$89.05	$89.00
Purchase #6	$94.35	7.179%	$101.1234	$101.12	$101.10	$101.10
Purchase #7	$179.84	7.655%	$193.6068	$193.61	$193.60	$193.60
7 purchase totals =	$875.74		$942.7649	$942.76	$942.70	$942.70