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	$249.94	10.550%	$276.3087	$276.31	$276.30	$276.30
Purchase #2	$45.31	13.853%	$51.5868	$51.59	$51.60	$51.60
Purchase #3	$148.35	11.802%	$165.8583	$165.86	$165.85	$165.90
Purchase #4	$161.48	13.624%	$183.48	$183.48	$183.50	$183.50
Purchase #5	$115.29	13.688%	$131.0709	$131.07	$131.05	$131.10
Purchase #6	$115.84	13.806%	$131.8329	$131.83	$131.85	$131.80
Purchase #7	$225.50	3.813%	$234.0983	$234.10	$234.10	$234.10
7 purchase totals =	$1,061.71		$1,174.2359	$1,174.24	$1,174.25	$1,174.30