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	$28.80	7.182%	$30.8684	$30.87	$30.85	$30.90
Purchase #2	$231.99	10.129%	$255.4883	$255.49	$255.50	$255.50
Purchase #3	$113.74	9.567%	$124.6215	$124.62	$124.60	$124.60
Purchase #4	$146.51	10.824%	$162.3682	$162.37	$162.35	$162.40
Purchase #5	$128.52	6.178%	$136.46	$136.46	$136.45	$136.50
Purchase #6	$190.92	4.571%	$199.647	$199.65	$199.65	$199.60
Purchase #7	$165.27	13.139%	$186.9848	$186.98	$187.00	$187.00
7 purchase totals =	$1,005.75		$1,096.4382	$1,096.44	$1,096.40	$1,096.50