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	$96.98	12.536%	$109.1374	$109.14	$109.15	$109.10
Purchase #2	$172.91	10.316%	$190.7474	$190.75	$190.75	$190.70
Purchase #3	$225.35	6.656%	$240.3493	$240.35	$240.35	$240.30
Purchase #4	$43.65	4.584%	$45.6509	$45.65	$45.65	$45.70
Purchase #5	$75.44	9.341%	$82.4869	$82.49	$82.50	$82.50
Purchase #6	$70.38	9.208%	$76.8606	$76.86	$76.85	$76.90
Purchase #7	$230.39	10.513%	$254.6109	$254.61	$254.60	$254.60
7 purchase totals =	$915.10		$999.8434	$999.85	$999.85	$999.80