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	$100.64	3.464%	$104.1262	$104.13	$104.15	$104.10
Purchase #2	$62.92	11.730%	$70.3005	$70.30	$70.30	$70.30
Purchase #3	$104.42	13.773%	$118.8018	$118.80	$118.80	$118.80
Purchase #4	$69.29	5.174%	$72.8751	$72.88	$72.90	$72.90
Purchase #5	$53.92	10.747%	$59.7148	$59.71	$59.70	$59.70
Purchase #6	$46.49	10.539%	$51.3896	$51.39	$51.40	$51.40
Purchase #7	$126.86	4.137%	$132.1082	$132.11	$132.10	$132.10
7 purchase totals =	$564.54		$609.3162	$609.32	$609.35	$609.30