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	$6.81	6.647%	$7.2627	$7.26	$7.25	$7.30
Purchase #2	$96.48	3.691%	$100.0411	$100.04	$100.05	$100.00
Purchase #3	$233.31	8.491%	$253.1204	$253.12	$253.10	$253.10
Purchase #4	$5.93	10.143%	$6.5315	$6.53	$6.55	$6.50
Purchase #5	$83.34	7.842%	$89.8755	$89.88	$89.90	$89.90
Purchase #6	$184.56	10.668%	$204.2489	$204.25	$204.25	$204.20
Purchase #7	$130.93	3.495%	$135.506	$135.51	$135.50	$135.50
7 purchase totals =	$741.36		$796.5861	$796.59	$796.60	$796.50