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	$30.73	5.295%	$32.3572	$32.36	$32.35	$32.40
Purchase #2	$242.60	12.651%	$273.2913	$273.29	$273.30	$273.30
Purchase #3	$84.84	5.249%	$89.2933	$89.29	$89.30	$89.30
Purchase #4	$130.69	5.411%	$137.7616	$137.76	$137.75	$137.80
Purchase #5	$211.45	10.531%	$233.7178	$233.72	$233.70	$233.70
Purchase #6	$11.40	8.552%	$12.3749	$12.37	$12.35	$12.40
Purchase #7	$177.48	7.461%	$190.7218	$190.72	$190.70	$190.70
7 purchase totals =	$889.19		$969.5179	$969.51	$969.45	$969.60