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	$186.54	6.354%	$198.3928	$198.39	$198.40	$198.40
Purchase #2	$169.88	10.306%	$187.3878	$187.39	$187.40	$187.40
Purchase #3	$132.33	5.211%	$139.2257	$139.23	$139.25	$139.20
Purchase #4	$138.46	10.243%	$152.6425	$152.64	$152.65	$152.60
Purchase #5	$151.39	9.629%	$165.9673	$165.97	$165.95	$166.00
Purchase #6	$103.26	7.778%	$111.2916	$111.29	$111.30	$111.30
Purchase #7	$167.75	13.474%	$190.3526	$190.35	$190.35	$190.40
7 purchase totals =	$1,049.61		$1,145.2603	$1,145.26	$1,145.30	$1,145.30