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	$101.35	7.861%	$109.3171	$109.32	$109.30	$109.30
Purchase #2	$119.40	3.722%	$123.8441	$123.84	$123.85	$123.80
Purchase #3	$144.35	8.830%	$157.0961	$157.10	$157.10	$157.10
Purchase #4	$237.72	6.786%	$253.8517	$253.85	$253.85	$253.90
Purchase #5	$226.71	11.198%	$252.097	$252.10	$252.10	$252.10
Purchase #6	$19.34	9.337%	$21.1458	$21.15	$21.15	$21.10
Purchase #7	$73.95	11.757%	$82.6443	$82.64	$82.65	$82.60
7 purchase totals =	$922.82		$999.9961	$1,000.00	$1,000.00	$999.90