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	$69.91	13.856%	$79.5967	$79.60	$79.60	$79.60
Purchase #2	$41.43	5.205%	$43.5864	$43.59	$43.60	$43.60
Purchase #3	$198.41	11.268%	$220.7668	$220.77	$220.75	$220.80
Purchase #4	$180.39	6.258%	$191.6788	$191.68	$191.70	$191.70
Purchase #5	$194.90	7.710%	$209.9268	$209.93	$209.95	$209.90
Purchase #6	$156.55	6.810%	$167.2111	$167.21	$167.20	$167.20
Purchase #7	$167.27	3.728%	$173.5058	$173.51	$173.50	$173.50
7 purchase totals =	$1,008.86		$1,086.2724	$1,086.29	$1,086.30	$1,086.30