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	$109.44	10.709%	$121.1599	$121.16	$121.15	$121.20
Purchase #2	$105.94	10.236%	$116.784	$116.78	$116.80	$116.80
Purchase #3	$190.37	11.303%	$211.8875	$211.89	$211.90	$211.90
Purchase #4	$19.57	6.831%	$20.9068	$20.91	$20.90	$20.90
Purchase #5	$138.43	11.163%	$153.8829	$153.88	$153.90	$153.90
Purchase #6	$104.51	3.870%	$108.5545	$108.55	$108.55	$108.60
Purchase #7	$78.81	8.826%	$85.7658	$85.77	$85.75	$85.80
7 purchase totals =	$747.07		$818.9414	$818.94	$818.95	$819.10