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	$17.51	11.853%	$19.5855	$19.59	$19.60	$19.60
Purchase #2	$245.27	3.348%	$253.4816	$253.48	$253.50	$253.50
Purchase #3	$218.68	6.591%	$233.0932	$233.09	$233.10	$233.10
Purchase #4	$232.38	7.205%	$249.123	$249.12	$249.10	$249.10
Purchase #5	$130.89	11.657%	$146.1478	$146.15	$146.15	$146.10
Purchase #6	$104.78	7.627%	$112.7716	$112.77	$112.75	$112.80
Purchase #7	$123.42	8.705%	$134.1637	$134.16	$134.15	$134.20
7 purchase totals =	$1,072.93		$1,148.3664	$1,148.36	$1,148.35	$1,148.40