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	$160.98	5.292%	$169.4991	$169.50	$169.50	$169.50
Purchase #2	$149.71	7.181%	$160.4607	$160.46	$160.45	$160.50
Purchase #3	$105.27	7.115%	$112.76	$112.76	$112.75	$112.80
Purchase #4	$121.85	4.304%	$127.0944	$127.09	$127.10	$127.10
Purchase #5	$169.86	4.185%	$176.9686	$176.97	$176.95	$177.00
Purchase #6	$186.25	7.612%	$200.4274	$200.43	$200.45	$200.40
Purchase #7	$37.94	5.864%	$40.1648	$40.16	$40.15	$40.20
7 purchase totals =	$931.86		$987.3750	$987.37	$987.35	$987.50