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	$45.72	13.661%	$51.9658	$51.97	$51.95	$52.00
Purchase #2	$187.77	8.816%	$204.3238	$204.32	$204.30	$204.30
Purchase #3	$126.36	4.355%	$131.863	$131.86	$131.85	$131.90
Purchase #4	$90.35	7.419%	$97.0531	$97.05	$97.05	$97.10
Purchase #5	$185.91	13.764%	$211.4987	$211.50	$211.50	$211.50
Purchase #6	$58.55	11.116%	$65.0584	$65.06	$65.05	$65.10
Purchase #7	$152.90	3.643%	$158.4701	$158.47	$158.45	$158.50
7 purchase totals =	$847.56		$920.2329	$920.23	$920.15	$920.40