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	$84.90	6.172%	$90.14	$90.14	$90.15	$90.10
Purchase #2	$249.80	10.306%	$275.5444	$275.54	$275.55	$275.50
Purchase #3	$80.46	3.456%	$83.2407	$83.24	$83.25	$83.20
Purchase #4	$154.59	11.539%	$172.4281	$172.43	$172.45	$172.40
Purchase #5	$239.53	9.174%	$261.5045	$261.50	$261.50	$261.50
Purchase #6	$45.30	3.337%	$46.8117	$46.81	$46.80	$46.80
Purchase #7	$163.36	8.172%	$176.7098	$176.71	$176.70	$176.70
7 purchase totals =	$1,017.94		$1,106.3792	$1,106.37	$1,106.40	$1,106.20