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	$105.35	10.641%	$116.5603	$116.56	$116.55	$116.60
Purchase #2	$26.59	4.201%	$27.707	$27.71	$27.70	$27.70
Purchase #3	$221.91	10.236%	$244.6247	$244.62	$244.60	$244.60
Purchase #4	$109.41	12.419%	$122.9976	$123.00	$123.00	$123.00
Purchase #5	$143.97	4.150%	$149.9448	$149.94	$149.95	$149.90
Purchase #6	$19.40	4.761%	$20.3236	$20.32	$20.30	$20.30
Purchase #7	$53.93	10.716%	$59.7091	$59.71	$59.70	$59.70
7 purchase totals =	$680.56		$741.8671	$741.86	$741.80	$741.80