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	$250.86	10.685%	$277.6644	$277.66	$277.65	$277.70
Purchase #2	$229.96	4.352%	$239.9679	$239.97	$239.95	$240.00
Purchase #3	$155.87	10.523%	$172.2722	$172.27	$172.25	$172.30
Purchase #4	$85.77	4.431%	$89.5705	$89.57	$89.55	$89.60
Purchase #5	$199.38	8.370%	$216.0681	$216.07	$216.05	$216.10
Purchase #6	$46.26	4.317%	$48.257	$48.26	$48.25	$48.30
Purchase #7	$96.75	3.261%	$99.905	$99.91	$99.90	$99.90
7 purchase totals =	$1,064.85		$1,143.7051	$1,143.71	$1,143.60	$1,143.90