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	$47.91	3.439%	$49.5576	$49.56	$49.55	$49.60
Purchase #2	$27.81	7.711%	$29.9544	$29.95	$29.95	$30.00
Purchase #3	$141.28	4.463%	$147.5853	$147.59	$147.60	$147.60
Purchase #4	$234.34	9.192%	$255.8805	$255.88	$255.90	$255.90
Purchase #5	$230.61	5.348%	$242.943	$242.94	$242.95	$242.90
Purchase #6	$236.51	13.658%	$268.8125	$268.81	$268.80	$268.80
Purchase #7	$58.85	12.556%	$66.2392	$66.24	$66.25	$66.20
7 purchase totals =	$977.31		$1,060.9725	$1,060.97	$1,061.00	$1,061.00