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	$7.26	9.129%	$7.9228	$7.92	$7.90	$7.90
Purchase #2	$220.30	3.637%	$228.3123	$228.31	$228.30	$228.30
Purchase #3	$211.60	7.224%	$226.886	$226.89	$226.90	$226.90
Purchase #4	$18.45	4.366%	$19.2555	$19.26	$19.25	$19.30
Purchase #5	$172.37	7.357%	$185.0513	$185.05	$185.05	$185.10
Purchase #6	$130.72	5.147%	$137.4482	$137.45	$137.45	$137.40
Purchase #7	$158.86	4.795%	$166.4773	$166.48	$166.50	$166.50
7 purchase totals =	$919.56		$971.3534	$971.36	$971.35	$971.40