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	$50.43	3.247%	$52.0675	$52.07	$52.05	$52.10
Purchase #2	$82.54	8.168%	$89.2819	$89.28	$89.30	$89.30
Purchase #3	$145.69	10.782%	$161.3983	$161.40	$161.40	$161.40
Purchase #4	$139.75	3.567%	$144.7349	$144.73	$144.75	$144.70
Purchase #5	$164.72	13.785%	$187.4267	$187.43	$187.45	$187.40
Purchase #6	$236.69	12.709%	$266.7709	$266.77	$266.75	$266.80
Purchase #7	$34.75	12.468%	$39.0826	$39.08	$39.10	$39.10
7 purchase totals =	$854.57		$940.7628	$940.76	$940.80	$940.80