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	$89.78	12.316%	$100.8373	$100.84	$100.85	$100.80
Purchase #2	$52.95	4.750%	$55.4651	$55.47	$55.45	$55.50
Purchase #3	$193.89	11.251%	$215.7046	$215.70	$215.70	$215.70
Purchase #4	$200.43	10.551%	$221.5774	$221.58	$221.60	$221.60
Purchase #5	$186.88	4.858%	$195.9586	$195.96	$195.95	$196.00
Purchase #6	$186.97	7.378%	$200.7646	$200.76	$200.75	$200.80
Purchase #7	$212.50	13.587%	$241.3724	$241.37	$241.35	$241.40
7 purchase totals =	$1,123.40		$1,231.6800	$1,231.68	$1,231.65	$1,231.80