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	$249.87	12.700%	$281.6035	$281.60	$281.60	$281.60
Purchase #2	$132.40	10.353%	$146.1074	$146.11	$146.10	$146.10
Purchase #3	$198.31	5.209%	$208.64	$208.64	$208.65	$208.60
Purchase #4	$77.41	11.685%	$86.4554	$86.46	$86.45	$86.50
Purchase #5	$50.38	4.396%	$52.5947	$52.59	$52.60	$52.60
Purchase #6	$92.80	8.324%	$100.5247	$100.52	$100.50	$100.50
Purchase #7	$21.97	11.251%	$24.4418	$24.44	$24.45	$24.40
7 purchase totals =	$823.14		$900.3675	$900.36	$900.35	$900.30