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	$137.45	7.230%	$147.3876	$147.39	$147.40	$147.40
Purchase #2	$131.71	13.588%	$149.6068	$149.61	$149.60	$149.60
Purchase #3	$68.32	10.405%	$75.4287	$75.43	$75.45	$75.40
Purchase #4	$37.81	7.157%	$40.5161	$40.52	$40.50	$40.50
Purchase #5	$54.79	9.204%	$59.8329	$59.83	$59.85	$59.80
Purchase #6	$185.26	13.567%	$210.3942	$210.39	$210.40	$210.40
Purchase #7	$83.94	7.456%	$90.1986	$90.20	$90.20	$90.20
7 purchase totals =	$699.28		$773.3649	$773.37	$773.40	$773.30