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	$11.63	8.177%	$12.581	$12.58	$12.60	$12.60
Purchase #2	$116.56	12.134%	$130.7034	$130.70	$130.70	$130.70
Purchase #3	$95.98	7.725%	$103.3945	$103.39	$103.40	$103.40
Purchase #4	$86.82	13.562%	$98.5945	$98.59	$98.60	$98.60
Purchase #5	$247.89	11.267%	$275.8198	$275.82	$275.80	$275.80
Purchase #6	$141.51	12.292%	$158.9044	$158.90	$158.90	$158.90
Purchase #7	$159.69	8.352%	$173.0273	$173.03	$173.05	$173.00
7 purchase totals =	$860.08		$953.0249	$953.01	$953.05	$953.00