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	$49.26	7.237%	$52.8249	$52.82	$52.80	$52.80
Purchase #2	$72.80	10.414%	$80.3814	$80.38	$80.40	$80.40
Purchase #3	$197.47	13.832%	$224.7841	$224.78	$224.80	$224.80
Purchase #4	$249.64	8.544%	$270.9692	$270.97	$270.95	$271.00
Purchase #5	$85.84	5.260%	$90.3552	$90.36	$90.35	$90.40
Purchase #6	$82.29	9.858%	$90.4021	$90.40	$90.40	$90.40
Purchase #7	$119.52	10.776%	$132.3995	$132.40	$132.40	$132.40
7 purchase totals =	$856.82		$942.1164	$942.11	$942.10	$942.20