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	$139.89	13.502%	$158.7779	$158.78	$158.80	$158.80
Purchase #2	$182.42	5.761%	$192.9292	$192.93	$192.95	$192.90
Purchase #3	$127.89	13.479%	$145.1283	$145.13	$145.15	$145.10
Purchase #4	$243.94	5.326%	$256.9322	$256.93	$256.95	$256.90
Purchase #5	$6.56	8.771%	$7.1354	$7.14	$7.15	$7.10
Purchase #6	$30.44	6.574%	$32.4411	$32.44	$32.45	$32.40
Purchase #7	$62.66	13.249%	$70.9618	$70.96	$70.95	$71.00
7 purchase totals =	$793.80		$864.3059	$864.31	$864.40	$864.20