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	$158.82	8.794%	$172.7866	$172.79	$172.80	$172.80
Purchase #2	$222.83	5.863%	$235.8945	$235.89	$235.90	$235.90
Purchase #3	$160.67	13.430%	$182.248	$182.25	$182.25	$182.20
Purchase #4	$102.53	9.185%	$111.9474	$111.95	$111.95	$111.90
Purchase #5	$215.73	3.333%	$222.9203	$222.92	$222.90	$222.90
Purchase #6	$138.76	6.691%	$148.0444	$148.04	$148.05	$148.00
Purchase #7	$70.48	9.521%	$77.1904	$77.19	$77.20	$77.20
7 purchase totals =	$1,069.82		$1,151.0316	$1,151.03	$1,151.05	$1,150.90