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	$121.50	5.124%	$127.7257	$127.73	$127.75	$127.70
Purchase #2	$50.85	10.451%	$56.1643	$56.16	$56.15	$56.20
Purchase #3	$199.36	10.645%	$220.5819	$220.58	$220.60	$220.60
Purchase #4	$60.82	4.254%	$63.4073	$63.41	$63.40	$63.40
Purchase #5	$159.80	11.485%	$178.153	$178.15	$178.15	$178.20
Purchase #6	$235.37	12.103%	$263.8568	$263.86	$263.85	$263.90
Purchase #7	$206.95	5.113%	$217.5314	$217.53	$217.55	$217.50
7 purchase totals =	$1,034.65		$1,127.4204	$1,127.42	$1,127.45	$1,127.50