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	$77.54	6.352%	$82.4653	$82.47	$82.45	$82.50
Purchase #2	$114.72	4.715%	$120.129	$120.13	$120.15	$120.10
Purchase #3	$140.95	5.650%	$148.9137	$148.91	$148.90	$148.90
Purchase #4	$25.49	8.341%	$27.6161	$27.62	$27.60	$27.60
Purchase #5	$81.76	13.238%	$92.5834	$92.58	$92.60	$92.60
Purchase #6	$219.61	13.388%	$249.0114	$249.01	$249.00	$249.00
Purchase #7	$128.56	11.493%	$143.3354	$143.34	$143.35	$143.30
7 purchase totals =	$788.63		$864.0543	$864.06	$864.05	$864.00