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	$40.86	10.326%	$45.0792	$45.08	$45.10	$45.10
Purchase #2	$160.70	7.602%	$172.9164	$172.92	$172.90	$172.90
Purchase #3	$158.78	5.225%	$167.0763	$167.08	$167.10	$167.10
Purchase #4	$73.44	7.373%	$78.8547	$78.85	$78.85	$78.90
Purchase #5	$114.74	6.389%	$122.0707	$122.07	$122.05	$122.10
Purchase #6	$31.91	10.577%	$35.2851	$35.29	$35.30	$35.30
Purchase #7	$216.46	5.547%	$228.467	$228.47	$228.45	$228.50
7 purchase totals =	$796.89		$849.7494	$849.76	$849.75	$849.90