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	$249.72	6.153%	$265.0853	$265.09	$265.10	$265.10
Purchase #2	$213.36	9.856%	$234.3888	$234.39	$234.40	$234.40
Purchase #3	$84.76	6.290%	$90.0914	$90.09	$90.10	$90.10
Purchase #4	$53.80	11.448%	$59.959	$59.96	$59.95	$60.00
Purchase #5	$47.35	11.568%	$52.8274	$52.83	$52.85	$52.80
Purchase #6	$207.83	4.656%	$217.5066	$217.51	$217.50	$217.50
Purchase #7	$240.58	13.590%	$273.2748	$273.27	$273.25	$273.30
7 purchase totals =	$1,097.40		$1,193.1333	$1,193.14	$1,193.15	$1,193.20