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	$211.73	12.672%	$238.5604	$238.56	$238.55	$238.60
Purchase #2	$132.81	13.291%	$150.4618	$150.46	$150.45	$150.50
Purchase #3	$164.31	8.537%	$178.3371	$178.34	$178.35	$178.30
Purchase #4	$80.76	11.337%	$89.9158	$89.92	$89.90	$89.90
Purchase #5	$40.66	4.223%	$42.3771	$42.38	$42.40	$42.40
Purchase #6	$24.83	8.191%	$26.8638	$26.86	$26.85	$26.90
Purchase #7	$19.61	4.740%	$20.5395	$20.54	$20.55	$20.50
7 purchase totals =	$674.71		$747.0555	$747.06	$747.05	$747.10