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	$240.82	6.105%	$255.5221	$255.52	$255.50	$255.50
Purchase #2	$32.97	13.175%	$37.3138	$37.31	$37.30	$37.30
Purchase #3	$42.36	4.623%	$44.3183	$44.32	$44.30	$44.30
Purchase #4	$54.35	13.437%	$61.653	$61.65	$61.65	$61.70
Purchase #5	$163.52	10.152%	$180.1206	$180.12	$180.10	$180.10
Purchase #6	$15.32	7.215%	$16.4253	$16.43	$16.45	$16.40
Purchase #7	$40.90	4.659%	$42.8055	$42.81	$42.80	$42.80
7 purchase totals =	$590.24		$638.1586	$638.16	$638.10	$638.10