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	$98.58	9.406%	$107.8524	$107.85	$107.85	$107.90
Purchase #2	$101.96	9.215%	$111.3556	$111.36	$111.35	$111.40
Purchase #3	$179.98	3.130%	$185.6134	$185.61	$185.60	$185.60
Purchase #4	$167.73	13.301%	$190.0398	$190.04	$190.05	$190.00
Purchase #5	$64.45	3.277%	$66.562	$66.56	$66.55	$66.60
Purchase #6	$42.28	11.362%	$47.0839	$47.08	$47.10	$47.10
Purchase #7	$97.75	7.746%	$105.3217	$105.32	$105.30	$105.30
7 purchase totals =	$752.73		$813.8288	$813.82	$813.80	$813.90