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	$59.55	12.182%	$66.8044	$66.80	$66.80	$66.80
Purchase #2	$250.86	9.856%	$275.5848	$275.58	$275.60	$275.60
Purchase #3	$33.58	12.574%	$37.8023	$37.80	$37.80	$37.80
Purchase #4	$239.42	10.453%	$264.4466	$264.45	$264.45	$264.40
Purchase #5	$75.67	13.637%	$85.9891	$85.99	$86.00	$86.00
Purchase #6	$189.50	10.220%	$208.8669	$208.87	$208.85	$208.90
Purchase #7	$78.28	4.576%	$81.8621	$81.86	$81.85	$81.90
7 purchase totals =	$926.86		$1,021.3562	$1,021.35	$1,021.35	$1,021.40