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	$198.51	13.583%	$225.4736	$225.47	$225.45	$225.50
Purchase #2	$28.53	8.198%	$30.8689	$30.87	$30.85	$30.90
Purchase #3	$116.33	13.403%	$131.9217	$131.92	$131.90	$131.90
Purchase #4	$24.74	4.325%	$25.81	$25.81	$25.80	$25.80
Purchase #5	$235.28	6.169%	$249.7944	$249.79	$249.80	$249.80
Purchase #6	$137.65	13.251%	$155.89	$155.89	$155.90	$155.90
Purchase #7	$38.94	5.137%	$40.9403	$40.94	$40.95	$40.90
7 purchase totals =	$779.98		$860.6989	$860.69	$860.65	$860.70