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	$134.57	6.850%	$143.788	$143.79	$143.80	$143.80
Purchase #2	$211.87	3.232%	$218.7176	$218.72	$218.70	$218.70
Purchase #3	$241.52	13.530%	$274.1977	$274.20	$274.20	$274.20
Purchase #4	$179.48	12.713%	$202.2973	$202.30	$202.30	$202.30
Purchase #5	$40.78	13.866%	$46.4346	$46.43	$46.45	$46.40
Purchase #6	$39.54	9.849%	$43.4343	$43.43	$43.45	$43.40
Purchase #7	$52.27	13.389%	$59.2684	$59.27	$59.25	$59.30
7 purchase totals =	$900.03		$988.1379	$988.14	$988.15	$988.10