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	$206.35	11.661%	$230.4125	$230.41	$230.40	$230.40
Purchase #2	$137.45	5.103%	$144.4641	$144.46	$144.45	$144.50
Purchase #3	$185.64	13.298%	$210.3264	$210.33	$210.35	$210.30
Purchase #4	$161.31	6.699%	$172.1162	$172.12	$172.10	$172.10
Purchase #5	$200.31	8.595%	$217.5266	$217.53	$217.55	$217.50
Purchase #6	$228.64	6.650%	$243.8446	$243.84	$243.85	$243.80
Purchase #7	$42.88	12.229%	$48.1238	$48.12	$48.10	$48.10
7 purchase totals =	$1,162.58		$1,266.8142	$1,266.81	$1,266.80	$1,266.70