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	$70.40	5.349%	$74.1657	$74.17	$74.15	$74.20
Purchase #2	$135.49	10.760%	$150.0687	$150.07	$150.05	$150.10
Purchase #3	$6.82	7.149%	$7.3076	$7.31	$7.30	$7.30
Purchase #4	$45.53	6.568%	$48.5204	$48.52	$48.50	$48.50
Purchase #5	$25.64	8.244%	$27.7538	$27.75	$27.75	$27.80
Purchase #6	$94.61	9.501%	$103.5989	$103.60	$103.60	$103.60
Purchase #7	$99.38	10.626%	$109.9401	$109.94	$109.95	$109.90
7 purchase totals =	$477.87		$521.3552	$521.36	$521.30	$521.40