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	$40.49	4.308%	$42.2343	$42.23	$42.25	$42.20
Purchase #2	$136.50	13.437%	$154.8415	$154.84	$154.85	$154.80
Purchase #3	$89.28	9.618%	$97.867	$97.87	$97.85	$97.90
Purchase #4	$134.49	9.246%	$146.9249	$146.92	$146.90	$146.90
Purchase #5	$235.44	10.230%	$259.5255	$259.53	$259.55	$259.50
Purchase #6	$247.57	7.670%	$266.5586	$266.56	$266.55	$266.60
Purchase #7	$44.60	6.523%	$47.5093	$47.51	$47.50	$47.50
7 purchase totals =	$928.37		$1,015.4611	$1,015.46	$1,015.45	$1,015.40