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	$105.89	5.109%	$111.2999	$111.30	$111.30	$111.30
Purchase #2	$171.84	5.813%	$181.8291	$181.83	$181.85	$181.80
Purchase #3	$44.52	7.318%	$47.778	$47.78	$47.80	$47.80
Purchase #4	$30.41	4.254%	$31.7036	$31.70	$31.70	$31.70
Purchase #5	$49.34	3.620%	$51.1261	$51.13	$51.15	$51.10
Purchase #6	$139.51	5.395%	$147.0366	$147.04	$147.05	$147.00
Purchase #7	$31.81	8.614%	$34.5501	$34.55	$34.55	$34.60
7 purchase totals =	$573.32		$605.3234	$605.33	$605.40	$605.30