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	$165.85	8.698%	$180.2756	$180.28	$180.30	$180.30
Purchase #2	$72.95	13.480%	$82.7837	$82.78	$82.80	$82.80
Purchase #3	$27.71	6.409%	$29.4859	$29.49	$29.50	$29.50
Purchase #4	$44.40	3.388%	$45.9043	$45.90	$45.90	$45.90
Purchase #5	$29.39	11.777%	$32.8513	$32.85	$32.85	$32.90
Purchase #6	$35.58	8.762%	$38.6975	$38.70	$38.70	$38.70
Purchase #7	$184.34	3.280%	$190.3864	$190.39	$190.40	$190.40
7 purchase totals =	$560.22		$600.3847	$600.39	$600.45	$600.50