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	$150.56	10.532%	$166.417	$166.42	$166.40	$166.40
Purchase #2	$164.44	6.787%	$175.6005	$175.60	$175.60	$175.60
Purchase #3	$169.54	10.647%	$187.5909	$187.59	$187.60	$187.60
Purchase #4	$127.85	7.571%	$137.5295	$137.53	$137.55	$137.50
Purchase #5	$41.84	13.430%	$47.4591	$47.46	$47.45	$47.50
Purchase #6	$234.55	13.615%	$266.484	$266.48	$266.50	$266.50
Purchase #7	$97.55	3.425%	$100.8911	$100.89	$100.90	$100.90
7 purchase totals =	$986.33		$1,081.9721	$1,081.97	$1,082.00	$1,082.00