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	$210.62	11.527%	$234.8982	$234.90	$234.90	$234.90
Purchase #2	$179.64	6.231%	$190.8334	$190.83	$190.85	$190.80
Purchase #3	$12.97	10.348%	$14.3121	$14.31	$14.30	$14.30
Purchase #4	$213.33	3.205%	$220.1672	$220.17	$220.15	$220.20
Purchase #5	$38.91	5.171%	$40.922	$40.92	$40.90	$40.90
Purchase #6	$47.59	12.612%	$53.5921	$53.59	$53.60	$53.60
Purchase #7	$59.38	11.823%	$66.4005	$66.40	$66.40	$66.40
7 purchase totals =	$762.44		$821.1255	$821.12	$821.10	$821.10