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	$72.32	7.699%	$77.8879	$77.89	$77.90	$77.90
Purchase #2	$69.30	12.672%	$78.0817	$78.08	$78.10	$78.10
Purchase #3	$19.69	9.606%	$21.5814	$21.58	$21.60	$21.60
Purchase #4	$43.31	11.682%	$48.3695	$48.37	$48.35	$48.40
Purchase #5	$7.69	7.460%	$8.2637	$8.26	$8.25	$8.30
Purchase #6	$227.73	9.607%	$249.608	$249.61	$249.60	$249.60
Purchase #7	$121.44	5.612%	$128.2552	$128.26	$128.25	$128.30
7 purchase totals =	$561.48		$612.0474	$612.05	$612.05	$612.20