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	$237.69	8.641%	$258.2288	$258.23	$258.25	$258.20
Purchase #2	$154.74	4.253%	$161.3211	$161.32	$161.30	$161.30
Purchase #3	$77.39	7.275%	$83.0201	$83.02	$83.00	$83.00
Purchase #4	$98.85	6.814%	$105.5856	$105.59	$105.60	$105.60
Purchase #5	$173.58	13.189%	$196.4735	$196.47	$196.45	$196.50
Purchase #6	$137.73	13.763%	$156.6858	$156.69	$156.70	$156.70
Purchase #7	$147.38	8.390%	$159.7452	$159.75	$159.75	$159.70
7 purchase totals =	$1,027.36		$1,121.0601	$1,121.07	$1,121.05	$1,121.00