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	$234.52	8.778%	$255.1062	$255.11	$255.10	$255.10
Purchase #2	$137.62	4.107%	$143.2721	$143.27	$143.25	$143.30
Purchase #3	$206.98	10.796%	$229.3256	$229.33	$229.35	$229.30
Purchase #4	$120.62	7.778%	$130.0018	$130.00	$130.00	$130.00
Purchase #5	$133.72	8.650%	$145.2868	$145.29	$145.30	$145.30
Purchase #6	$53.56	9.123%	$58.4463	$58.45	$58.45	$58.40
Purchase #7	$75.45	12.836%	$85.1348	$85.13	$85.15	$85.10
7 purchase totals =	$962.47		$1,046.5736	$1,046.58	$1,046.60	$1,046.50