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	$96.77	3.863%	$100.5082	$100.51	$100.50	$100.50
Purchase #2	$149.72	3.139%	$154.4197	$154.42	$154.40	$154.40
Purchase #3	$95.51	5.769%	$101.02	$101.02	$101.00	$101.00
Purchase #4	$22.38	11.769%	$25.0139	$25.01	$25.00	$25.00
Purchase #5	$38.60	12.646%	$43.4814	$43.48	$43.50	$43.50
Purchase #6	$178.51	4.836%	$187.1427	$187.14	$187.15	$187.10
Purchase #7	$149.66	6.326%	$159.1275	$159.13	$159.15	$159.10
7 purchase totals =	$731.15		$770.7134	$770.71	$770.70	$770.60