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	$145.64	4.798%	$152.6278	$152.63	$152.65	$152.60
Purchase #2	$107.72	4.523%	$112.5922	$112.59	$112.60	$112.60
Purchase #3	$78.36	8.510%	$85.0284	$85.03	$85.05	$85.00
Purchase #4	$14.75	12.439%	$16.5848	$16.58	$16.60	$16.60
Purchase #5	$147.35	11.722%	$164.6224	$164.62	$164.60	$164.60
Purchase #6	$37.87	7.243%	$40.6129	$40.61	$40.60	$40.60
Purchase #7	$12.30	4.193%	$12.8157	$12.82	$12.80	$12.80
7 purchase totals =	$543.99		$584.8842	$584.88	$584.90	$584.80