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	$249.83	11.263%	$277.9684	$277.97	$277.95	$278.00
Purchase #2	$116.62	12.393%	$131.0727	$131.07	$131.05	$131.10
Purchase #3	$144.47	4.726%	$151.2977	$151.30	$151.30	$151.30
Purchase #4	$244.98	4.664%	$256.4059	$256.41	$256.40	$256.40
Purchase #5	$157.55	4.321%	$164.3577	$164.36	$164.35	$164.40
Purchase #6	$164.78	4.235%	$171.7584	$171.76	$171.75	$171.80
Purchase #7	$28.92	3.538%	$29.9432	$29.94	$29.95	$29.90
7 purchase totals =	$1,107.15		$1,182.8040	$1,182.81	$1,182.75	$1,182.90