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	$21.55	13.510%	$24.4614	$24.46	$24.45	$24.50
Purchase #2	$75.96	9.236%	$82.9757	$82.98	$83.00	$83.00
Purchase #3	$88.96	4.102%	$92.6091	$92.61	$92.60	$92.60
Purchase #4	$18.89	10.111%	$20.8	$20.80	$20.80	$20.80
Purchase #5	$98.27	13.620%	$111.6544	$111.65	$111.65	$111.70
Purchase #6	$186.75	12.751%	$210.5625	$210.56	$210.55	$210.60
Purchase #7	$36.34	9.745%	$39.8813	$39.88	$39.90	$39.90
7 purchase totals =	$526.72		$582.9444	$582.94	$582.95	$583.10