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	$35.43	10.645%	$39.2015	$39.20	$39.20	$39.20
Purchase #2	$37.53	5.352%	$39.5386	$39.54	$39.55	$39.50
Purchase #3	$248.74	10.776%	$275.5442	$275.54	$275.55	$275.50
Purchase #4	$64.78	6.144%	$68.7601	$68.76	$68.75	$68.80
Purchase #5	$70.70	11.503%	$78.8326	$78.83	$78.85	$78.80
Purchase #6	$71.46	10.461%	$78.9354	$78.94	$78.95	$78.90
Purchase #7	$225.77	4.354%	$235.6	$235.60	$235.60	$235.60
7 purchase totals =	$754.41		$816.4124	$816.41	$816.45	$816.30