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	$194.81	12.714%	$219.5781	$219.58	$219.60	$219.60
Purchase #2	$137.40	9.544%	$150.5135	$150.51	$150.50	$150.50
Purchase #3	$66.76	7.642%	$71.8618	$71.86	$71.85	$71.90
Purchase #4	$64.36	10.494%	$71.1139	$71.11	$71.10	$71.10
Purchase #5	$47.34	8.684%	$51.451	$51.45	$51.45	$51.50
Purchase #6	$172.38	9.186%	$188.2148	$188.21	$188.20	$188.20
Purchase #7	$23.45	8.123%	$25.3548	$25.35	$25.35	$25.40
7 purchase totals =	$706.50		$778.0879	$778.07	$778.05	$778.20