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	$154.91	10.548%	$171.2499	$171.25	$171.25	$171.20
Purchase #2	$139.83	5.546%	$147.585	$147.59	$147.60	$147.60
Purchase #3	$130.36	3.469%	$134.8822	$134.88	$134.90	$134.90
Purchase #4	$105.25	10.835%	$116.6538	$116.65	$116.65	$116.70
Purchase #5	$148.51	13.155%	$168.0465	$168.05	$168.05	$168.00
Purchase #6	$18.79	4.717%	$19.6763	$19.68	$19.70	$19.70
Purchase #7	$56.89	9.440%	$62.2604	$62.26	$62.25	$62.30
7 purchase totals =	$754.54		$820.3541	$820.36	$820.40	$820.40