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	$162.87	8.298%	$176.385	$176.39	$176.40	$176.40
Purchase #2	$150.34	5.142%	$158.0705	$158.07	$158.05	$158.10
Purchase #3	$185.90	4.684%	$194.6076	$194.61	$194.60	$194.60
Purchase #4	$74.44	12.513%	$83.7547	$83.75	$83.75	$83.80
Purchase #5	$20.60	4.444%	$21.5155	$21.52	$21.50	$21.50
Purchase #6	$109.98	12.321%	$123.5306	$123.53	$123.55	$123.50
Purchase #7	$223.46	7.521%	$240.2664	$240.27	$240.25	$240.30
7 purchase totals =	$927.59		$998.1303	$998.14	$998.10	$998.20