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	$76.81	4.827%	$80.5176	$80.52	$80.50	$80.50
Purchase #2	$9.94	13.833%	$11.315	$11.32	$11.30	$11.30
Purchase #3	$130.98	13.240%	$148.3218	$148.32	$148.30	$148.30
Purchase #4	$33.70	12.440%	$37.8923	$37.89	$37.90	$37.90
Purchase #5	$51.86	4.619%	$54.2554	$54.26	$54.25	$54.30
Purchase #6	$125.61	5.562%	$132.5964	$132.60	$132.60	$132.60
Purchase #7	$75.57	12.354%	$84.9059	$84.91	$84.90	$84.90
7 purchase totals =	$504.47		$549.8044	$549.82	$549.75	$549.80