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	$213.49	6.537%	$227.4458	$227.45	$227.45	$227.40
Purchase #2	$201.27	9.224%	$219.8351	$219.84	$219.85	$219.80
Purchase #3	$158.91	4.140%	$165.4889	$165.49	$165.50	$165.50
Purchase #4	$92.99	11.386%	$103.5778	$103.58	$103.60	$103.60
Purchase #5	$220.69	7.191%	$236.5598	$236.56	$236.55	$236.60
Purchase #6	$85.71	7.791%	$92.3877	$92.39	$92.40	$92.40
Purchase #7	$230.96	10.474%	$255.1508	$255.15	$255.15	$255.20
7 purchase totals =	$1,204.02		$1,300.4459	$1,300.46	$1,300.50	$1,300.50