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	$18.56	9.716%	$20.3633	$20.36	$20.35	$20.40
Purchase #2	$148.36	13.748%	$168.7565	$168.76	$168.75	$168.80
Purchase #3	$128.81	12.418%	$144.8056	$144.81	$144.80	$144.80
Purchase #4	$191.29	4.761%	$200.3973	$200.40	$200.40	$200.40
Purchase #5	$209.81	6.126%	$222.663	$222.66	$222.65	$222.70
Purchase #6	$238.39	9.243%	$260.4244	$260.42	$260.40	$260.40
Purchase #7	$191.62	7.630%	$206.2406	$206.24	$206.25	$206.20
7 purchase totals =	$1,126.84		$1,223.6507	$1,223.65	$1,223.60	$1,223.70