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	$108.65	10.833%	$120.4201	$120.42	$120.40	$120.40
Purchase #2	$25.93	9.181%	$28.3106	$28.31	$28.30	$28.30
Purchase #3	$59.78	11.777%	$66.8203	$66.82	$66.80	$66.80
Purchase #4	$49.45	6.374%	$52.6019	$52.60	$52.60	$52.60
Purchase #5	$89.37	10.304%	$98.5787	$98.58	$98.60	$98.60
Purchase #6	$57.99	6.269%	$61.6254	$61.63	$61.65	$61.60
Purchase #7	$157.74	9.665%	$172.9856	$172.99	$173.00	$173.00
7 purchase totals =	$548.91		$601.3426	$601.35	$601.35	$601.30