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	$8.96	12.694%	$10.0974	$10.10	$10.10	$10.10
Purchase #2	$247.60	3.175%	$255.4613	$255.46	$255.45	$255.50
Purchase #3	$181.80	3.848%	$188.7957	$188.80	$188.80	$188.80
Purchase #4	$96.33	9.396%	$105.3812	$105.38	$105.40	$105.40
Purchase #5	$130.34	3.839%	$135.3438	$135.34	$135.35	$135.30
Purchase #6	$48.37	8.107%	$52.2914	$52.29	$52.30	$52.30
Purchase #7	$51.33	6.688%	$54.763	$54.76	$54.75	$54.80
7 purchase totals =	$764.73		$802.1338	$802.13	$802.15	$802.20