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	$31.81	6.113%	$33.7545	$33.75	$33.75	$33.80
Purchase #2	$78.65	8.850%	$85.6105	$85.61	$85.60	$85.60
Purchase #3	$172.36	5.648%	$182.0949	$182.09	$182.10	$182.10
Purchase #4	$82.87	13.271%	$93.8677	$93.87	$93.85	$93.90
Purchase #5	$127.45	7.700%	$137.2637	$137.26	$137.25	$137.30
Purchase #6	$205.89	11.559%	$229.6888	$229.69	$229.70	$229.70
Purchase #7	$115.70	3.330%	$119.5528	$119.55	$119.55	$119.60
7 purchase totals =	$814.73		$881.8329	$881.82	$881.80	$882.00