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	$144.45	9.472%	$158.1323	$158.13	$158.15	$158.10
Purchase #2	$93.77	6.321%	$99.6972	$99.70	$99.70	$99.70
Purchase #3	$20.50	3.473%	$21.212	$21.21	$21.20	$21.20
Purchase #4	$184.50	5.291%	$194.2619	$194.26	$194.25	$194.30
Purchase #5	$55.77	3.304%	$57.6126	$57.61	$57.60	$57.60
Purchase #6	$42.77	4.872%	$44.8538	$44.85	$44.85	$44.90
Purchase #7	$166.54	13.141%	$188.425	$188.43	$188.45	$188.40
7 purchase totals =	$708.30		$764.1948	$764.19	$764.20	$764.20