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	$74.94	13.580%	$85.1169	$85.12	$85.10	$85.10
Purchase #2	$111.46	13.790%	$126.8303	$126.83	$126.85	$126.80
Purchase #3	$45.78	12.437%	$51.4737	$51.47	$51.45	$51.50
Purchase #4	$119.90	3.256%	$123.8039	$123.80	$123.80	$123.80
Purchase #5	$15.85	3.741%	$16.4429	$16.44	$16.45	$16.40
Purchase #6	$209.61	11.850%	$234.4488	$234.45	$234.45	$234.40
Purchase #7	$49.47	5.702%	$52.2908	$52.29	$52.30	$52.30
7 purchase totals =	$627.01		$690.4073	$690.40	$690.40	$690.30