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	$19.36	11.502%	$21.5868	$21.59	$21.60	$21.60
Purchase #2	$51.89	9.847%	$56.9996	$57.00	$57.00	$57.00
Purchase #3	$188.74	9.555%	$206.7741	$206.77	$206.75	$206.80
Purchase #4	$51.34	7.725%	$55.306	$55.31	$55.30	$55.30
Purchase #5	$45.86	4.140%	$47.7586	$47.76	$47.75	$47.80
Purchase #6	$73.80	12.423%	$82.9682	$82.97	$82.95	$83.00
Purchase #7	$238.32	7.191%	$255.4576	$255.46	$255.45	$255.50
7 purchase totals =	$669.31		$726.8509	$726.86	$726.80	$727.00