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	$58.91	8.502%	$63.9185	$63.92	$63.90	$63.90
Purchase #2	$46.85	11.561%	$52.2663	$52.27	$52.25	$52.30
Purchase #3	$35.44	12.636%	$39.9182	$39.92	$39.90	$39.90
Purchase #4	$126.37	5.225%	$132.9728	$132.97	$132.95	$133.00
Purchase #5	$208.46	8.146%	$225.4412	$225.44	$225.45	$225.40
Purchase #6	$95.70	3.743%	$99.2821	$99.28	$99.30	$99.30
Purchase #7	$37.51	7.791%	$40.4324	$40.43	$40.45	$40.40
7 purchase totals =	$609.24		$654.2315	$654.23	$654.20	$654.20