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	$31.45	4.306%	$32.8042	$32.80	$32.80	$32.80
Purchase #2	$191.97	13.327%	$217.5538	$217.55	$217.55	$217.60
Purchase #3	$29.34	13.709%	$33.3622	$33.36	$33.35	$33.40
Purchase #4	$208.84	11.501%	$232.8587	$232.86	$232.85	$232.90
Purchase #5	$27.99	5.766%	$29.6039	$29.60	$29.60	$29.60
Purchase #6	$52.70	13.557%	$59.8445	$59.84	$59.85	$59.80
Purchase #7	$178.72	10.143%	$196.8476	$196.85	$196.85	$196.80
7 purchase totals =	$721.01		$802.8749	$802.86	$802.85	$802.90