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	$89.45	9.138%	$97.6239	$97.62	$97.60	$97.60
Purchase #2	$221.47	13.300%	$250.9255	$250.93	$250.95	$250.90
Purchase #3	$139.88	3.820%	$145.2234	$145.22	$145.20	$145.20
Purchase #4	$66.58	12.544%	$74.9318	$74.93	$74.95	$74.90
Purchase #5	$58.76	4.159%	$61.2038	$61.20	$61.20	$61.20
Purchase #6	$162.87	5.371%	$171.6177	$171.62	$171.60	$171.60
Purchase #7	$50.76	7.585%	$54.6101	$54.61	$54.60	$54.60
7 purchase totals =	$789.77		$856.1362	$856.13	$856.10	$856.00