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	$227.71	5.599%	$240.4595	$240.46	$240.45	$240.50
Purchase #2	$54.99	3.388%	$56.8531	$56.85	$56.85	$56.90
Purchase #3	$160.50	6.345%	$170.6837	$170.68	$170.70	$170.70
Purchase #4	$198.29	9.717%	$217.5578	$217.56	$217.55	$217.60
Purchase #5	$74.99	13.465%	$85.0874	$85.09	$85.10	$85.10
Purchase #6	$239.65	11.807%	$267.9455	$267.95	$267.95	$267.90
Purchase #7	$40.82	4.800%	$42.7794	$42.78	$42.80	$42.80
7 purchase totals =	$996.95		$1,081.3664	$1,081.37	$1,081.40	$1,081.50