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	$240.92	6.228%	$255.9245	$255.92	$255.90	$255.90
Purchase #2	$98.77	9.751%	$108.4011	$108.40	$108.40	$108.40
Purchase #3	$177.86	7.397%	$191.0163	$191.02	$191.00	$191.00
Purchase #4	$121.51	6.812%	$129.7873	$129.79	$129.80	$129.80
Purchase #5	$95.40	13.461%	$108.2418	$108.24	$108.25	$108.20
Purchase #6	$92.76	13.304%	$105.1008	$105.10	$105.10	$105.10
Purchase #7	$33.30	6.537%	$35.4768	$35.48	$35.50	$35.50
7 purchase totals =	$860.52		$933.9486	$933.95	$933.95	$933.90