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	$93.26	9.322%	$101.9537	$101.95	$101.95	$102.00
Purchase #2	$227.89	12.297%	$255.9136	$255.91	$255.90	$255.90
Purchase #3	$185.30	8.105%	$200.3186	$200.32	$200.30	$200.30
Purchase #4	$123.72	10.819%	$137.1053	$137.11	$137.10	$137.10
Purchase #5	$128.76	7.576%	$138.5149	$138.51	$138.50	$138.50
Purchase #6	$164.82	10.201%	$181.6333	$181.63	$181.65	$181.60
Purchase #7	$66.67	11.327%	$74.2217	$74.22	$74.20	$74.20
7 purchase totals =	$990.42		$1,089.6611	$1,089.65	$1,089.60	$1,089.60