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	$178.92	3.865%	$185.8353	$185.84	$185.85	$185.80
Purchase #2	$47.39	9.530%	$51.9063	$51.91	$51.90	$51.90
Purchase #3	$147.70	13.141%	$167.1093	$167.11	$167.10	$167.10
Purchase #4	$238.37	3.867%	$247.5878	$247.59	$247.60	$247.60
Purchase #5	$85.86	7.397%	$92.2111	$92.21	$92.20	$92.20
Purchase #6	$97.52	12.298%	$109.513	$109.51	$109.50	$109.50
Purchase #7	$59.43	11.226%	$66.1016	$66.10	$66.10	$66.10
7 purchase totals =	$855.19		$920.2644	$920.27	$920.25	$920.20