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	$78.85	9.263%	$86.1539	$86.15	$86.15	$86.20
Purchase #2	$55.93	10.626%	$61.8731	$61.87	$61.85	$61.90
Purchase #3	$36.33	10.188%	$40.0313	$40.03	$40.05	$40.00
Purchase #4	$187.67	12.390%	$210.9223	$210.92	$210.90	$210.90
Purchase #5	$108.57	12.249%	$121.8687	$121.87	$121.85	$121.90
Purchase #6	$53.31	11.324%	$59.3468	$59.35	$59.35	$59.30
Purchase #7	$53.58	11.221%	$59.5922	$59.59	$59.60	$59.60
7 purchase totals =	$574.24		$639.7883	$639.78	$639.75	$639.80