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	$78.52	13.711%	$89.2859	$89.29	$89.30	$89.30
Purchase #2	$59.92	13.463%	$67.987	$67.99	$68.00	$68.00
Purchase #3	$191.93	3.615%	$198.8683	$198.87	$198.85	$198.90
Purchase #4	$91.31	4.453%	$95.376	$95.38	$95.40	$95.40
Purchase #5	$110.70	11.448%	$123.3729	$123.37	$123.35	$123.40
Purchase #6	$138.58	4.554%	$144.8909	$144.89	$144.90	$144.90
Purchase #7	$195.52	12.629%	$220.2122	$220.21	$220.20	$220.20
7 purchase totals =	$866.48		$939.9932	$940.00	$940.00	$940.10