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	$91.47	8.224%	$98.9925	$98.99	$99.00	$99.00
Purchase #2	$9.49	13.697%	$10.7898	$10.79	$10.80	$10.80
Purchase #3	$233.68	9.379%	$255.5968	$255.60	$255.60	$255.60
Purchase #4	$204.72	8.606%	$222.3382	$222.34	$222.35	$222.30
Purchase #5	$241.69	13.505%	$274.3302	$274.33	$274.35	$274.30
Purchase #6	$33.37	5.870%	$35.3288	$35.33	$35.35	$35.30
Purchase #7	$174.50	10.224%	$192.3409	$192.34	$192.35	$192.30
7 purchase totals =	$988.92		$1,089.7172	$1,089.72	$1,089.80	$1,089.60