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	$55.29	12.280%	$62.0796	$62.08	$62.10	$62.10
Purchase #2	$132.52	7.267%	$142.1502	$142.15	$142.15	$142.20
Purchase #3	$154.26	11.499%	$171.9984	$172.00	$172.00	$172.00
Purchase #4	$136.84	5.146%	$143.8818	$143.88	$143.90	$143.90
Purchase #5	$169.93	12.272%	$190.7838	$190.78	$190.80	$190.80
Purchase #6	$101.63	9.825%	$111.6151	$111.62	$111.60	$111.60
Purchase #7	$48.44	7.853%	$52.244	$52.24	$52.25	$52.20
7 purchase totals =	$798.91		$874.7529	$874.75	$874.80	$874.80