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	$68.67	13.795%	$78.143	$78.14	$78.15	$78.10
Purchase #2	$180.55	4.401%	$188.496	$188.50	$188.50	$188.50
Purchase #3	$46.78	13.710%	$53.1935	$53.19	$53.20	$53.20
Purchase #4	$140.98	9.188%	$153.9332	$153.93	$153.95	$153.90
Purchase #5	$10.60	8.300%	$11.4798	$11.48	$11.50	$11.50
Purchase #6	$175.82	5.620%	$185.7011	$185.70	$185.70	$185.70
Purchase #7	$56.31	7.586%	$60.5817	$60.58	$60.60	$60.60
7 purchase totals =	$679.71		$731.5283	$731.52	$731.60	$731.50