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	$104.64	11.492%	$116.6652	$116.67	$116.65	$116.70
Purchase #2	$28.30	13.668%	$32.168	$32.17	$32.15	$32.20
Purchase #3	$120.52	8.130%	$130.3183	$130.32	$130.30	$130.30
Purchase #4	$188.27	13.176%	$213.0765	$213.08	$213.10	$213.10
Purchase #5	$14.53	10.761%	$16.0936	$16.09	$16.10	$16.10
Purchase #6	$32.83	13.715%	$37.3326	$37.33	$37.35	$37.30
Purchase #7	$37.81	5.551%	$39.9088	$39.91	$39.90	$39.90
7 purchase totals =	$526.90		$585.5630	$585.57	$585.55	$585.60