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	$31.50	13.763%	$35.8353	$35.84	$35.85	$35.80
Purchase #2	$120.79	9.138%	$131.8278	$131.83	$131.85	$131.80
Purchase #3	$12.55	3.556%	$12.9963	$13.00	$13.00	$13.00
Purchase #4	$211.56	7.361%	$227.1329	$227.13	$227.15	$227.10
Purchase #5	$187.40	9.349%	$204.92	$204.92	$204.90	$204.90
Purchase #6	$229.29	10.847%	$254.1611	$254.16	$254.15	$254.20
Purchase #7	$80.87	11.119%	$89.8619	$89.86	$89.85	$89.90
7 purchase totals =	$873.96		$956.7353	$956.74	$956.75	$956.70