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	$133.54	4.178%	$139.1193	$139.12	$139.10	$139.10
Purchase #2	$181.78	8.161%	$196.6151	$196.62	$196.60	$196.60
Purchase #3	$97.70	9.456%	$106.9385	$106.94	$106.95	$106.90
Purchase #4	$110.34	7.450%	$118.5603	$118.56	$118.55	$118.60
Purchase #5	$240.73	11.737%	$268.9845	$268.98	$269.00	$269.00
Purchase #6	$132.55	10.754%	$146.8044	$146.80	$146.80	$146.80
Purchase #7	$80.27	7.789%	$86.5222	$86.52	$86.50	$86.50
7 purchase totals =	$976.91		$1,063.5443	$1,063.54	$1,063.50	$1,063.50