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	$90.55	9.690%	$99.3243	$99.32	$99.30	$99.30
Purchase #2	$45.52	6.333%	$48.4028	$48.40	$48.40	$48.40
Purchase #3	$199.81	10.200%	$220.1906	$220.19	$220.20	$220.20
Purchase #4	$207.68	8.693%	$225.7336	$225.73	$225.75	$225.70
Purchase #5	$86.86	5.282%	$91.4479	$91.45	$91.45	$91.40
Purchase #6	$74.27	5.557%	$78.3972	$78.40	$78.40	$78.40
Purchase #7	$194.67	10.147%	$214.4232	$214.42	$214.40	$214.40
7 purchase totals =	$899.36		$977.9196	$977.91	$977.90	$977.80