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	$32.66	8.650%	$35.4851	$35.49	$35.50	$35.50
Purchase #2	$30.68	13.848%	$34.9286	$34.93	$34.95	$34.90
Purchase #3	$96.26	3.508%	$99.6368	$99.64	$99.65	$99.60
Purchase #4	$115.97	9.818%	$127.3559	$127.36	$127.35	$127.40
Purchase #5	$135.83	11.770%	$151.8172	$151.82	$151.80	$151.80
Purchase #6	$44.84	8.361%	$48.5891	$48.59	$48.60	$48.60
Purchase #7	$98.26	11.242%	$109.3064	$109.31	$109.30	$109.30
7 purchase totals =	$554.50		$607.1191	$607.14	$607.15	$607.10