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	$50.54	12.649%	$56.9328	$56.93	$56.95	$56.90
Purchase #2	$152.38	12.594%	$171.5707	$171.57	$171.55	$171.60
Purchase #3	$51.72	10.632%	$57.2189	$57.22	$57.20	$57.20
Purchase #4	$42.80	13.330%	$48.5052	$48.51	$48.50	$48.50
Purchase #5	$200.56	9.269%	$219.1499	$219.15	$219.15	$219.10
Purchase #6	$245.72	13.345%	$278.5113	$278.51	$278.50	$278.50
Purchase #7	$195.68	12.816%	$220.7583	$220.76	$220.75	$220.80
7 purchase totals =	$939.40		$1,052.6471	$1,052.65	$1,052.60	$1,052.60