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	$40.83	13.365%	$46.2869	$46.29	$46.30	$46.30
Purchase #2	$241.96	6.804%	$258.423	$258.42	$258.40	$258.40
Purchase #3	$174.88	7.732%	$188.4017	$188.40	$188.40	$188.40
Purchase #4	$20.72	5.322%	$21.8227	$21.82	$21.80	$21.80
Purchase #5	$50.39	6.377%	$53.6034	$53.60	$53.60	$53.60
Purchase #6	$128.65	11.564%	$143.5271	$143.53	$143.55	$143.50
Purchase #7	$7.39	10.664%	$8.1781	$8.18	$8.20	$8.20
7 purchase totals =	$664.82		$720.2429	$720.24	$720.25	$720.20