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	$250.83	6.316%	$266.6724	$266.67	$266.65	$266.70
Purchase #2	$122.89	12.127%	$137.7929	$137.79	$137.80	$137.80
Purchase #3	$73.84	11.767%	$82.5288	$82.53	$82.55	$82.50
Purchase #4	$54.75	9.504%	$59.9534	$59.95	$59.95	$60.00
Purchase #5	$168.29	7.684%	$181.2214	$181.22	$181.20	$181.20
Purchase #6	$137.40	12.513%	$154.5929	$154.59	$154.60	$154.60
Purchase #7	$92.29	12.730%	$104.0385	$104.04	$104.05	$104.00
7 purchase totals =	$900.29		$986.8003	$986.79	$986.80	$986.80