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	$79.67	12.105%	$89.3141	$89.31	$89.30	$89.30
Purchase #2	$231.50	12.709%	$260.9213	$260.92	$260.90	$260.90
Purchase #3	$167.82	10.576%	$185.5686	$185.57	$185.55	$185.60
Purchase #4	$39.45	3.679%	$40.9014	$40.90	$40.90	$40.90
Purchase #5	$170.77	3.498%	$176.7435	$176.74	$176.75	$176.70
Purchase #6	$140.27	9.145%	$153.0977	$153.10	$153.10	$153.10
Purchase #7	$239.62	8.820%	$260.7545	$260.75	$260.75	$260.80
7 purchase totals =	$1,069.10		$1,167.3011	$1,167.29	$1,167.25	$1,167.30