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	$249.80	12.833%	$281.8568	$281.86	$281.85	$281.90
Purchase #2	$216.37	12.460%	$243.3297	$243.33	$243.35	$243.30
Purchase #3	$135.66	7.482%	$145.8101	$145.81	$145.80	$145.80
Purchase #4	$31.45	3.720%	$32.6199	$32.62	$32.60	$32.60
Purchase #5	$89.52	13.399%	$101.5148	$101.51	$101.50	$101.50
Purchase #6	$71.82	11.158%	$79.8337	$79.83	$79.85	$79.80
Purchase #7	$24.45	12.491%	$27.504	$27.50	$27.50	$27.50
7 purchase totals =	$819.07		$912.4690	$912.46	$912.45	$912.40