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	$79.60	11.808%	$88.9992	$89.00	$89.00	$89.00
Purchase #2	$240.98	5.293%	$253.7351	$253.74	$253.75	$253.70
Purchase #3	$118.87	10.826%	$131.7389	$131.74	$131.75	$131.70
Purchase #4	$106.61	4.720%	$111.642	$111.64	$111.65	$111.60
Purchase #5	$117.49	7.703%	$126.5403	$126.54	$126.55	$126.50
Purchase #6	$38.49	3.449%	$39.8175	$39.82	$39.80	$39.80
Purchase #7	$188.39	12.807%	$212.5171	$212.52	$212.50	$212.50
7 purchase totals =	$890.43		$964.9901	$965.00	$965.00	$964.80