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	$136.99	3.498%	$141.7819	$141.78	$141.80	$141.80
Purchase #2	$220.78	3.405%	$228.2976	$228.30	$228.30	$228.30
Purchase #3	$31.26	13.791%	$35.5711	$35.57	$35.55	$35.60
Purchase #4	$87.45	9.749%	$95.9755	$95.98	$96.00	$96.00
Purchase #5	$209.29	6.492%	$222.8771	$222.88	$222.90	$222.90
Purchase #6	$11.84	4.644%	$12.3898	$12.39	$12.40	$12.40
Purchase #7	$114.52	11.375%	$127.5467	$127.55	$127.55	$127.50
7 purchase totals =	$812.13		$864.4397	$864.45	$864.50	$864.50