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	$41.53	9.778%	$45.5908	$45.59	$45.60	$45.60
Purchase #2	$105.37	12.505%	$118.5465	$118.55	$118.55	$118.50
Purchase #3	$38.82	8.743%	$42.214	$42.21	$42.20	$42.20
Purchase #4	$46.52	9.228%	$50.8129	$50.81	$50.80	$50.80
Purchase #5	$90.42	13.494%	$102.6213	$102.62	$102.60	$102.60
Purchase #6	$195.55	13.662%	$222.266	$222.27	$222.25	$222.30
Purchase #7	$217.79	7.395%	$233.8956	$233.90	$233.90	$233.90
7 purchase totals =	$736.00		$815.9471	$815.95	$815.90	$815.90