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	$101.64	7.721%	$109.4876	$109.49	$109.50	$109.50
Purchase #2	$45.86	13.690%	$52.1382	$52.14	$52.15	$52.10
Purchase #3	$96.58	12.831%	$108.9722	$108.97	$108.95	$109.00
Purchase #4	$148.67	6.733%	$158.68	$158.68	$158.70	$158.70
Purchase #5	$161.78	4.226%	$168.6168	$168.62	$168.60	$168.60
Purchase #6	$201.61	13.258%	$228.3395	$228.34	$228.35	$228.30
Purchase #7	$96.69	7.419%	$103.8634	$103.86	$103.85	$103.90
7 purchase totals =	$852.83		$930.0977	$930.10	$930.10	$930.10