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	$47.73	11.634%	$53.2829	$53.28	$53.30	$53.30
Purchase #2	$86.55	4.558%	$90.4949	$90.49	$90.50	$90.50
Purchase #3	$59.95	12.856%	$67.6572	$67.66	$67.65	$67.70
Purchase #4	$104.48	11.365%	$116.3542	$116.35	$116.35	$116.40
Purchase #5	$107.40	13.248%	$121.6284	$121.63	$121.65	$121.60
Purchase #6	$172.26	13.415%	$195.3687	$195.37	$195.35	$195.40
Purchase #7	$99.71	9.784%	$109.4656	$109.47	$109.45	$109.50
7 purchase totals =	$678.08		$754.2519	$754.25	$754.25	$754.40