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	$156.82	8.793%	$170.6092	$170.61	$170.60	$170.60
Purchase #2	$37.32	6.257%	$39.6551	$39.66	$39.65	$39.70
Purchase #3	$40.55	3.147%	$41.8261	$41.83	$41.85	$41.80
Purchase #4	$161.33	6.820%	$172.3327	$172.33	$172.35	$172.30
Purchase #5	$223.87	11.160%	$248.8539	$248.85	$248.85	$248.90
Purchase #6	$59.41	11.331%	$66.1417	$66.14	$66.15	$66.10
Purchase #7	$209.97	3.831%	$218.014	$218.01	$218.00	$218.00
7 purchase totals =	$889.27		$957.4327	$957.43	$957.45	$957.40