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	$84.74	5.204%	$89.1499	$89.15	$89.15	$89.10
Purchase #2	$101.72	9.384%	$111.2654	$111.27	$111.25	$111.30
Purchase #3	$241.45	9.378%	$264.0932	$264.09	$264.10	$264.10
Purchase #4	$15.33	4.327%	$15.9933	$15.99	$16.00	$16.00
Purchase #5	$111.55	3.179%	$115.0962	$115.10	$115.10	$115.10
Purchase #6	$104.63	4.548%	$109.3886	$109.39	$109.40	$109.40
Purchase #7	$15.64	5.358%	$16.478	$16.48	$16.50	$16.50
7 purchase totals =	$675.06		$721.4646	$721.47	$721.50	$721.50