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	$223.93	6.585%	$238.6758	$238.68	$238.70	$238.70
Purchase #2	$180.31	4.284%	$188.0345	$188.03	$188.05	$188.00
Purchase #3	$74.83	7.244%	$80.2507	$80.25	$80.25	$80.30
Purchase #4	$105.50	7.704%	$113.6277	$113.63	$113.65	$113.60
Purchase #5	$157.69	13.193%	$178.494	$178.49	$178.50	$178.50
Purchase #6	$91.28	11.582%	$101.852	$101.85	$101.85	$101.90
Purchase #7	$165.58	8.574%	$179.7768	$179.78	$179.80	$179.80
7 purchase totals =	$999.12		$1,080.7115	$1,080.71	$1,080.80	$1,080.80