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	$53.59	10.205%	$59.0589	$59.06	$59.05	$59.10
Purchase #2	$133.49	5.738%	$141.1497	$141.15	$141.15	$141.10
Purchase #3	$18.55	13.169%	$20.9928	$20.99	$21.00	$21.00
Purchase #4	$123.51	11.102%	$137.2221	$137.22	$137.20	$137.20
Purchase #5	$73.75	4.154%	$76.8136	$76.81	$76.80	$76.80
Purchase #6	$195.91	6.227%	$208.1093	$208.11	$208.10	$208.10
Purchase #7	$91.42	9.355%	$99.9723	$99.97	$99.95	$100.00
7 purchase totals =	$690.22		$743.3187	$743.31	$743.25	$743.30