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	$112.83	4.228%	$117.6005	$117.60	$117.60	$117.60
Purchase #2	$95.64	13.466%	$108.5189	$108.52	$108.50	$108.50
Purchase #3	$119.78	11.275%	$133.2852	$133.29	$133.30	$133.30
Purchase #4	$209.91	10.335%	$231.6042	$231.60	$231.60	$231.60
Purchase #5	$147.49	10.385%	$162.8068	$162.81	$162.80	$162.80
Purchase #6	$53.98	7.341%	$57.9427	$57.94	$57.95	$57.90
Purchase #7	$250.99	9.609%	$275.1076	$275.11	$275.10	$275.10
7 purchase totals =	$990.62		$1,086.8659	$1,086.87	$1,086.85	$1,086.80