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	$194.36	3.201%	$200.5815	$200.58	$200.60	$200.60
Purchase #2	$122.80	12.563%	$138.2274	$138.23	$138.25	$138.20
Purchase #3	$243.44	5.374%	$256.5225	$256.52	$256.50	$256.50
Purchase #4	$81.33	11.232%	$90.465	$90.47	$90.45	$90.50
Purchase #5	$113.61	12.730%	$128.0726	$128.07	$128.05	$128.10
Purchase #6	$70.95	12.870%	$80.0813	$80.08	$80.10	$80.10
Purchase #7	$232.28	10.236%	$256.0562	$256.06	$256.05	$256.10
7 purchase totals =	$1,058.77		$1,150.0065	$1,150.01	$1,150.00	$1,150.10