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	$225.45	13.856%	$256.6884	$256.69	$256.70	$256.70
Purchase #2	$51.76	9.545%	$56.7005	$56.70	$56.70	$56.70
Purchase #3	$109.41	13.291%	$123.9517	$123.95	$123.95	$124.00
Purchase #4	$37.43	12.654%	$42.1664	$42.17	$42.15	$42.20
Purchase #5	$147.26	10.252%	$162.3571	$162.36	$162.35	$162.40
Purchase #6	$155.50	7.699%	$167.4719	$167.47	$167.45	$167.50
Purchase #7	$79.88	11.311%	$88.9152	$88.92	$88.90	$88.90
7 purchase totals =	$806.69		$898.2512	$898.26	$898.20	$898.40