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	$231.52	8.229%	$250.5718	$250.57	$250.55	$250.60
Purchase #2	$113.92	8.697%	$123.8276	$123.83	$123.85	$123.80
Purchase #3	$47.46	9.514%	$51.9753	$51.98	$52.00	$52.00
Purchase #4	$51.55	11.151%	$57.2983	$57.30	$57.30	$57.30
Purchase #5	$117.83	3.243%	$121.6512	$121.65	$121.65	$121.70
Purchase #6	$241.68	12.311%	$271.4332	$271.43	$271.45	$271.40
Purchase #7	$246.84	11.465%	$275.1402	$275.14	$275.15	$275.10
7 purchase totals =	$1,050.80		$1,151.8976	$1,151.90	$1,151.95	$1,151.90