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	$28.75	10.722%	$31.8326	$31.83	$31.85	$31.80
Purchase #2	$198.79	10.403%	$219.4701	$219.47	$219.45	$219.50
Purchase #3	$170.50	4.576%	$178.3021	$178.30	$178.30	$178.30
Purchase #4	$208.62	5.589%	$220.2798	$220.28	$220.30	$220.30
Purchase #5	$177.85	7.572%	$191.3168	$191.32	$191.30	$191.30
Purchase #6	$78.43	11.620%	$87.5436	$87.54	$87.55	$87.50
Purchase #7	$70.40	7.759%	$75.8623	$75.86	$75.85	$75.90
7 purchase totals =	$933.34		$1,004.6073	$1,004.60	$1,004.60	$1,004.60