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	$29.37	11.148%	$32.6442	$32.64	$32.65	$32.60
Purchase #2	$152.38	13.741%	$173.3185	$173.32	$173.30	$173.30
Purchase #3	$39.36	10.775%	$43.601	$43.60	$43.60	$43.60
Purchase #4	$175.99	5.205%	$185.1503	$185.15	$185.15	$185.20
Purchase #5	$125.38	10.138%	$138.091	$138.09	$138.10	$138.10
Purchase #6	$221.60	3.735%	$229.8768	$229.88	$229.90	$229.90
Purchase #7	$120.85	11.377%	$134.5991	$134.60	$134.60	$134.60
7 purchase totals =	$864.93		$937.2809	$937.28	$937.30	$937.30