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	$160.70	4.107%	$167.2999	$167.30	$167.30	$167.30
Purchase #2	$143.74	11.658%	$160.4972	$160.50	$160.50	$160.50
Purchase #3	$19.85	4.370%	$20.7174	$20.72	$20.70	$20.70
Purchase #4	$235.86	5.171%	$248.0563	$248.06	$248.05	$248.10
Purchase #5	$141.99	6.735%	$151.553	$151.55	$151.55	$151.60
Purchase #6	$45.52	11.741%	$50.8645	$50.86	$50.85	$50.90
Purchase #7	$120.69	6.537%	$128.5795	$128.58	$128.60	$128.60
7 purchase totals =	$868.35		$927.5678	$927.57	$927.55	$927.70