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	$229.41	11.818%	$256.5217	$256.52	$256.50	$256.50
Purchase #2	$21.45	12.275%	$24.083	$24.08	$24.10	$24.10
Purchase #3	$33.73	13.388%	$38.2458	$38.25	$38.25	$38.20
Purchase #4	$209.56	6.219%	$222.5925	$222.59	$222.60	$222.60
Purchase #5	$112.51	13.524%	$127.7259	$127.73	$127.75	$127.70
Purchase #6	$138.52	12.214%	$155.4388	$155.44	$155.45	$155.40
Purchase #7	$54.68	8.209%	$59.1687	$59.17	$59.15	$59.20
7 purchase totals =	$799.86		$883.7764	$883.78	$883.80	$883.70