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	$80.61	11.269%	$89.6939	$89.69	$89.70	$89.70
Purchase #2	$74.69	4.487%	$78.0413	$78.04	$78.05	$78.00
Purchase #3	$81.30	11.141%	$90.3576	$90.36	$90.35	$90.40
Purchase #4	$249.96	10.226%	$275.5209	$275.52	$275.50	$275.50
Purchase #5	$155.42	3.778%	$161.2918	$161.29	$161.30	$161.30
Purchase #6	$179.35	9.373%	$196.1605	$196.16	$196.15	$196.20
Purchase #7	$95.39	9.166%	$104.1334	$104.13	$104.15	$104.10
7 purchase totals =	$916.72		$995.1994	$995.19	$995.20	$995.20