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	$138.99	10.837%	$154.0523	$154.05	$154.05	$154.10
Purchase #2	$71.25	9.694%	$78.157	$78.16	$78.15	$78.20
Purchase #3	$128.63	9.245%	$140.5218	$140.52	$140.50	$140.50
Purchase #4	$104.53	9.450%	$114.4081	$114.41	$114.40	$114.40
Purchase #5	$144.90	6.399%	$154.1722	$154.17	$154.15	$154.20
Purchase #6	$85.45	6.348%	$90.8744	$90.87	$90.85	$90.90
Purchase #7	$184.61	4.496%	$192.9101	$192.91	$192.90	$192.90
7 purchase totals =	$858.36		$925.0959	$925.09	$925.00	$925.20