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	$117.38	10.324%	$129.4983	$129.50	$129.50	$129.50
Purchase #2	$85.32	5.672%	$90.1594	$90.16	$90.15	$90.20
Purchase #3	$228.34	5.606%	$241.1407	$241.14	$241.15	$241.10
Purchase #4	$25.95	11.179%	$28.851	$28.85	$28.85	$28.90
Purchase #5	$41.50	11.153%	$46.1285	$46.13	$46.15	$46.10
Purchase #6	$37.89	12.381%	$42.5812	$42.58	$42.60	$42.60
Purchase #7	$192.77	9.860%	$211.7771	$211.78	$211.80	$211.80
7 purchase totals =	$729.15		$790.1362	$790.14	$790.20	$790.20