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	$219.66	9.613%	$240.7759	$240.78	$240.80	$240.80
Purchase #2	$243.32	7.475%	$261.5082	$261.51	$261.50	$261.50
Purchase #3	$183.60	10.444%	$202.7752	$202.78	$202.80	$202.80
Purchase #4	$241.56	9.463%	$264.4188	$264.42	$264.40	$264.40
Purchase #5	$53.56	5.275%	$56.3853	$56.39	$56.40	$56.40
Purchase #6	$88.87	13.577%	$100.9359	$100.94	$100.95	$100.90
Purchase #7	$139.74	10.212%	$154.0102	$154.01	$154.00	$154.00
7 purchase totals =	$1,170.31		$1,280.8095	$1,280.83	$1,280.85	$1,280.80