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	$209.87	7.341%	$225.2766	$225.28	$225.30	$225.30
Purchase #2	$146.85	12.803%	$165.6512	$165.65	$165.65	$165.70
Purchase #3	$107.25	13.335%	$121.5518	$121.55	$121.55	$121.60
Purchase #4	$47.52	5.761%	$50.2576	$50.26	$50.25	$50.30
Purchase #5	$54.52	3.520%	$56.4391	$56.44	$56.45	$56.40
Purchase #6	$215.42	3.478%	$222.9123	$222.91	$222.90	$222.90
Purchase #7	$105.55	5.389%	$111.2381	$111.24	$111.25	$111.20
7 purchase totals =	$886.98		$953.3267	$953.33	$953.35	$953.40