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	$81.92	10.419%	$90.4552	$90.46	$90.45	$90.50
Purchase #2	$145.52	5.673%	$153.7753	$153.78	$153.80	$153.80
Purchase #3	$81.56	10.721%	$90.304	$90.30	$90.30	$90.30
Purchase #4	$35.39	13.506%	$40.1698	$40.17	$40.15	$40.20
Purchase #5	$203.26	7.405%	$218.3114	$218.31	$218.30	$218.30
Purchase #6	$211.51	11.820%	$236.5105	$236.51	$236.50	$236.50
Purchase #7	$47.98	5.301%	$50.5234	$50.52	$50.50	$50.50
7 purchase totals =	$807.14		$880.0496	$880.05	$880.00	$880.10