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	$58.76	13.113%	$66.4652	$66.47	$66.45	$66.50
Purchase #2	$119.40	10.438%	$131.863	$131.86	$131.85	$131.90
Purchase #3	$206.65	11.173%	$229.739	$229.74	$229.75	$229.70
Purchase #4	$100.50	4.643%	$105.1662	$105.17	$105.15	$105.20
Purchase #5	$87.35	11.402%	$97.3096	$97.31	$97.30	$97.30
Purchase #6	$95.57	5.299%	$100.6343	$100.63	$100.65	$100.60
Purchase #7	$134.86	5.245%	$141.9334	$141.93	$141.95	$141.90
7 purchase totals =	$803.09		$873.1107	$873.11	$873.10	$873.10