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	$235.89	8.200%	$255.233	$255.23	$255.25	$255.20
Purchase #2	$128.28	12.670%	$144.5331	$144.53	$144.55	$144.50
Purchase #3	$135.61	11.459%	$151.1495	$151.15	$151.15	$151.10
Purchase #4	$181.82	12.316%	$204.213	$204.21	$204.20	$204.20
Purchase #5	$149.61	11.497%	$166.8107	$166.81	$166.80	$166.80
Purchase #6	$14.91	4.515%	$15.5832	$15.58	$15.60	$15.60
Purchase #7	$39.90	3.712%	$41.3811	$41.38	$41.40	$41.40
7 purchase totals =	$886.02		$978.9036	$978.89	$978.95	$978.80