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	$91.97	10.692%	$101.8034	$101.80	$101.80	$101.80
Purchase #2	$115.54	4.787%	$121.0709	$121.07	$121.05	$121.10
Purchase #3	$116.99	5.361%	$123.2618	$123.26	$123.25	$123.30
Purchase #4	$74.82	9.738%	$82.106	$82.11	$82.10	$82.10
Purchase #5	$240.45	6.384%	$255.8003	$255.80	$255.80	$255.80
Purchase #6	$29.77	11.272%	$33.1257	$33.13	$33.15	$33.10
Purchase #7	$136.71	12.456%	$153.7386	$153.74	$153.75	$153.70
7 purchase totals =	$806.25		$870.9067	$870.91	$870.90	$870.90