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	$161.36	10.830%	$178.8353	$178.84	$178.85	$178.80
Purchase #2	$93.90	7.259%	$100.7162	$100.72	$100.70	$100.70
Purchase #3	$212.40	6.353%	$225.8938	$225.89	$225.90	$225.90
Purchase #4	$37.66	7.869%	$40.6235	$40.62	$40.60	$40.60
Purchase #5	$239.63	10.612%	$265.0595	$265.06	$265.05	$265.10
Purchase #6	$223.85	5.810%	$236.8557	$236.86	$236.85	$236.90
Purchase #7	$152.65	13.295%	$172.9448	$172.94	$172.95	$172.90
7 purchase totals =	$1,121.45		$1,220.9288	$1,220.93	$1,220.90	$1,220.90