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	$250.26	13.874%	$284.9811	$284.98	$285.00	$285.00
Purchase #2	$39.42	6.298%	$41.9027	$41.90	$41.90	$41.90
Purchase #3	$147.32	8.617%	$160.0146	$160.01	$160.00	$160.00
Purchase #4	$151.54	5.530%	$159.9202	$159.92	$159.90	$159.90
Purchase #5	$246.40	6.569%	$262.586	$262.59	$262.60	$262.60
Purchase #6	$111.34	13.304%	$126.1527	$126.15	$126.15	$126.20
Purchase #7	$128.29	12.703%	$144.5867	$144.59	$144.60	$144.60
7 purchase totals =	$1,074.57		$1,180.1440	$1,180.14	$1,180.15	$1,180.20