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	$27.92	6.465%	$29.725	$29.73	$29.75	$29.70
Purchase #2	$164.77	8.508%	$178.7886	$178.79	$178.80	$178.80
Purchase #3	$147.25	7.737%	$158.6427	$158.64	$158.65	$158.60
Purchase #4	$41.45	4.473%	$43.3041	$43.30	$43.30	$43.30
Purchase #5	$97.44	4.260%	$101.5909	$101.59	$101.60	$101.60
Purchase #6	$46.89	9.102%	$51.1579	$51.16	$51.15	$51.20
Purchase #7	$78.42	6.340%	$83.3918	$83.39	$83.40	$83.40
7 purchase totals =	$604.14		$646.6010	$646.60	$646.65	$646.60