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	$50.87	9.424%	$55.664	$55.66	$55.65	$55.70
Purchase #2	$104.82	12.832%	$118.2705	$118.27	$118.25	$118.30
Purchase #3	$122.33	12.378%	$137.472	$137.47	$137.45	$137.50
Purchase #4	$49.57	9.827%	$54.4412	$54.44	$54.45	$54.40
Purchase #5	$72.27	8.789%	$78.6218	$78.62	$78.60	$78.60
Purchase #6	$166.99	4.349%	$174.2524	$174.25	$174.25	$174.30
Purchase #7	$5.39	11.487%	$6.0091	$6.01	$6.00	$6.00
7 purchase totals =	$572.24		$624.7310	$624.72	$624.65	$624.80