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	$16.52	12.653%	$18.6103	$18.61	$18.60	$18.60
Purchase #2	$97.95	7.805%	$105.595	$105.60	$105.60	$105.60
Purchase #3	$57.31	9.489%	$62.7481	$62.75	$62.75	$62.70
Purchase #4	$41.91	9.588%	$45.9283	$45.93	$45.95	$45.90
Purchase #5	$93.53	6.296%	$99.4186	$99.42	$99.40	$99.40
Purchase #6	$222.34	3.583%	$230.3064	$230.31	$230.30	$230.30
Purchase #7	$225.42	8.476%	$244.5266	$244.53	$244.55	$244.50
7 purchase totals =	$754.98		$807.1333	$807.15	$807.15	$807.00