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	$43.83	10.748%	$48.5408	$48.54	$48.55	$48.50
Purchase #2	$132.53	5.349%	$139.619	$139.62	$139.60	$139.60
Purchase #3	$82.51	10.275%	$90.9879	$90.99	$91.00	$91.00
Purchase #4	$184.62	4.602%	$193.1162	$193.12	$193.10	$193.10
Purchase #5	$81.47	10.120%	$89.7148	$89.71	$89.70	$89.70
Purchase #6	$5.54	10.268%	$6.1088	$6.11	$6.10	$6.10
Purchase #7	$40.58	8.236%	$43.9222	$43.92	$43.90	$43.90
7 purchase totals =	$571.08		$612.0097	$612.01	$611.95	$611.90