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	$248.35	12.723%	$279.9476	$279.95	$279.95	$279.90
Purchase #2	$86.94	4.143%	$90.5419	$90.54	$90.55	$90.50
Purchase #3	$134.65	8.717%	$146.3874	$146.39	$146.40	$146.40
Purchase #4	$38.89	9.178%	$42.4593	$42.46	$42.45	$42.50
Purchase #5	$169.57	10.563%	$187.4817	$187.48	$187.50	$187.50
Purchase #6	$249.76	7.786%	$269.2063	$269.21	$269.20	$269.20
Purchase #7	$32.57	5.793%	$34.4568	$34.46	$34.45	$34.50
7 purchase totals =	$960.73		$1,050.4810	$1,050.49	$1,050.50	$1,050.50