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	$127.88	12.843%	$144.3036	$144.30	$144.30	$144.30
Purchase #2	$50.46	6.359%	$53.6688	$53.67	$53.65	$53.70
Purchase #3	$106.71	11.349%	$118.8205	$118.82	$118.80	$118.80
Purchase #4	$166.61	3.277%	$172.0698	$172.07	$172.05	$172.10
Purchase #5	$73.69	9.240%	$80.499	$80.50	$80.50	$80.50
Purchase #6	$33.94	13.727%	$38.5989	$38.60	$38.60	$38.60
Purchase #7	$62.34	8.369%	$67.5572	$67.56	$67.55	$67.60
7 purchase totals =	$621.63		$675.5178	$675.52	$675.45	$675.60