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	$11.47	7.827%	$12.3678	$12.37	$12.35	$12.40
Purchase #2	$140.65	13.410%	$159.5112	$159.51	$159.50	$159.50
Purchase #3	$72.65	10.163%	$80.0334	$80.03	$80.05	$80.00
Purchase #4	$77.38	7.279%	$83.0125	$83.01	$83.00	$83.00
Purchase #5	$40.47	12.324%	$45.4575	$45.46	$45.45	$45.50
Purchase #6	$161.99	7.780%	$174.5928	$174.59	$174.60	$174.60
Purchase #7	$160.51	7.525%	$172.5884	$172.59	$172.60	$172.60
7 purchase totals =	$665.12		$727.5636	$727.56	$727.55	$727.60