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	$39.96	5.321%	$42.0863	$42.09	$42.10	$42.10
Purchase #2	$136.77	6.701%	$145.935	$145.94	$145.95	$145.90
Purchase #3	$59.73	8.218%	$64.6386	$64.64	$64.65	$64.60
Purchase #4	$131.77	12.585%	$148.3533	$148.35	$148.35	$148.40
Purchase #5	$134.56	13.715%	$153.0149	$153.01	$153.00	$153.00
Purchase #6	$95.47	5.543%	$100.7619	$100.76	$100.75	$100.80
Purchase #7	$152.80	3.792%	$158.5942	$158.59	$158.60	$158.60
7 purchase totals =	$751.06		$813.3842	$813.38	$813.40	$813.40