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	$168.71	5.799%	$178.4935	$178.49	$178.50	$178.50
Purchase #2	$126.63	5.249%	$133.2768	$133.28	$133.30	$133.30
Purchase #3	$94.52	7.252%	$101.3746	$101.37	$101.35	$101.40
Purchase #4	$65.71	8.576%	$71.3453	$71.35	$71.35	$71.30
Purchase #5	$82.45	3.742%	$85.5353	$85.54	$85.55	$85.50
Purchase #6	$105.96	11.204%	$117.8318	$117.83	$117.85	$117.80
Purchase #7	$93.52	10.865%	$103.6809	$103.68	$103.70	$103.70
7 purchase totals =	$737.50		$791.5382	$791.54	$791.60	$791.50