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	$19.87	10.260%	$21.9087	$21.91	$21.90	$21.90
Purchase #2	$51.99	13.155%	$58.8293	$58.83	$58.85	$58.80
Purchase #3	$60.60	11.408%	$67.5132	$67.51	$67.50	$67.50
Purchase #4	$20.98	8.519%	$22.7673	$22.77	$22.75	$22.80
Purchase #5	$61.34	8.236%	$66.392	$66.39	$66.40	$66.40
Purchase #6	$33.58	11.534%	$37.4531	$37.45	$37.45	$37.50
Purchase #7	$215.40	13.749%	$245.0153	$245.02	$245.00	$245.00
7 purchase totals =	$463.76		$519.8789	$519.88	$519.85	$519.90