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	$100.34	11.510%	$111.8891	$111.89	$111.90	$111.90
Purchase #2	$149.54	12.220%	$167.8138	$167.81	$167.80	$167.80
Purchase #3	$57.95	5.777%	$61.2978	$61.30	$61.30	$61.30
Purchase #4	$32.83	8.689%	$35.6826	$35.68	$35.70	$35.70
Purchase #5	$207.46	7.389%	$222.7892	$222.79	$222.80	$222.80
Purchase #6	$153.55	13.243%	$173.8846	$173.88	$173.90	$173.90
Purchase #7	$112.70	7.467%	$121.1153	$121.12	$121.10	$121.10
7 purchase totals =	$814.37		$894.4724	$894.47	$894.50	$894.50