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	$102.54	8.649%	$111.4087	$111.41	$111.40	$111.40
Purchase #2	$226.25	13.664%	$257.1648	$257.16	$257.15	$257.20
Purchase #3	$148.56	8.760%	$161.5739	$161.57	$161.55	$161.60
Purchase #4	$77.39	4.379%	$80.7789	$80.78	$80.80	$80.80
Purchase #5	$196.80	7.363%	$211.2904	$211.29	$211.30	$211.30
Purchase #6	$44.35	3.600%	$45.9466	$45.95	$45.95	$45.90
Purchase #7	$63.59	10.749%	$70.4253	$70.43	$70.45	$70.40
7 purchase totals =	$859.48		$938.5886	$938.59	$938.60	$938.60