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	$53.32	4.498%	$55.7183	$55.72	$55.70	$55.70
Purchase #2	$63.78	13.544%	$72.4184	$72.42	$72.40	$72.40
Purchase #3	$132.70	13.522%	$150.6437	$150.64	$150.65	$150.60
Purchase #4	$54.80	12.153%	$61.4598	$61.46	$61.45	$61.50
Purchase #5	$249.36	12.373%	$280.2133	$280.21	$280.20	$280.20
Purchase #6	$179.32	12.406%	$201.5664	$201.57	$201.55	$201.60
Purchase #7	$12.70	11.516%	$14.1625	$14.16	$14.15	$14.20
7 purchase totals =	$745.98		$836.1824	$836.18	$836.10	$836.20