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	$53.50	9.367%	$58.5113	$58.51	$58.50	$58.50
Purchase #2	$42.40	5.160%	$44.5878	$44.59	$44.60	$44.60
Purchase #3	$237.50	7.723%	$255.8421	$255.84	$255.85	$255.80
Purchase #4	$19.63	11.521%	$21.8916	$21.89	$21.90	$21.90
Purchase #5	$31.58	11.711%	$35.2783	$35.28	$35.30	$35.30
Purchase #6	$25.49	10.233%	$28.0984	$28.10	$28.10	$28.10
Purchase #7	$151.82	4.813%	$159.1271	$159.13	$159.15	$159.10
7 purchase totals =	$561.92		$603.3366	$603.34	$603.40	$603.30