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	$135.88	5.666%	$143.579	$143.58	$143.60	$143.60
Purchase #2	$149.28	13.809%	$169.8941	$169.89	$169.90	$169.90
Purchase #3	$155.37	4.221%	$161.9282	$161.93	$161.95	$161.90
Purchase #4	$104.88	6.317%	$111.5053	$111.51	$111.50	$111.50
Purchase #5	$86.33	8.117%	$93.3374	$93.34	$93.35	$93.30
Purchase #6	$11.83	10.208%	$13.0376	$13.04	$13.05	$13.00
Purchase #7	$127.68	5.395%	$134.5683	$134.57	$134.55	$134.60
7 purchase totals =	$771.25		$827.8499	$827.86	$827.90	$827.80