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	$147.83	4.335%	$154.2384	$154.24	$154.25	$154.20
Purchase #2	$190.41	8.625%	$206.8329	$206.83	$206.85	$206.80
Purchase #3	$176.73	5.485%	$186.4236	$186.42	$186.40	$186.40
Purchase #4	$7.83	8.117%	$8.4656	$8.47	$8.45	$8.50
Purchase #5	$248.61	12.627%	$280.002	$280.00	$280.00	$280.00
Purchase #6	$148.50	13.484%	$168.5237	$168.52	$168.50	$168.50
Purchase #7	$12.31	6.866%	$13.1552	$13.16	$13.15	$13.20
7 purchase totals =	$932.22		$1,017.6414	$1,017.64	$1,017.60	$1,017.60