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	$148.77	13.324%	$168.5921	$168.59	$168.60	$168.60
Purchase #2	$68.98	13.680%	$78.4165	$78.42	$78.40	$78.40
Purchase #3	$165.78	13.220%	$187.6961	$187.70	$187.70	$187.70
Purchase #4	$85.75	5.831%	$90.7501	$90.75	$90.75	$90.80
Purchase #5	$136.69	10.355%	$150.8442	$150.84	$150.85	$150.80
Purchase #6	$221.94	12.131%	$248.8635	$248.86	$248.85	$248.90
Purchase #7	$50.70	6.356%	$53.9225	$53.92	$53.90	$53.90
7 purchase totals =	$878.61		$979.0850	$979.08	$979.05	$979.10