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	$159.57	6.400%	$169.7825	$169.78	$169.80	$169.80
Purchase #2	$92.28	13.850%	$105.0608	$105.06	$105.05	$105.10
Purchase #3	$182.68	6.497%	$194.5487	$194.55	$194.55	$194.50
Purchase #4	$52.73	4.763%	$55.2415	$55.24	$55.25	$55.20
Purchase #5	$38.36	4.540%	$40.1015	$40.10	$40.10	$40.10
Purchase #6	$216.36	10.327%	$238.7035	$238.70	$238.70	$238.70
Purchase #7	$205.48	5.677%	$217.1451	$217.15	$217.15	$217.10
7 purchase totals =	$947.46		$1,020.5836	$1,020.58	$1,020.60	$1,020.50