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	$52.35	6.202%	$55.5967	$55.60	$55.60	$55.60
Purchase #2	$49.41	7.843%	$53.2852	$53.29	$53.30	$53.30
Purchase #3	$165.82	5.710%	$175.2883	$175.29	$175.30	$175.30
Purchase #4	$63.35	7.231%	$67.9308	$67.93	$67.95	$67.90
Purchase #5	$230.99	3.230%	$238.451	$238.45	$238.45	$238.50
Purchase #6	$118.83	4.380%	$124.0348	$124.03	$124.05	$124.00
Purchase #7	$200.56	11.803%	$224.2321	$224.23	$224.25	$224.20
7 purchase totals =	$881.31		$938.8189	$938.82	$938.90	$938.80