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	$121.99	4.269%	$127.1978	$127.20	$127.20	$127.20
Purchase #2	$161.43	11.315%	$179.6958	$179.70	$179.70	$179.70
Purchase #3	$120.89	13.256%	$136.9152	$136.92	$136.90	$136.90
Purchase #4	$33.48	13.836%	$38.1123	$38.11	$38.10	$38.10
Purchase #5	$106.32	11.870%	$118.9402	$118.94	$118.95	$118.90
Purchase #6	$71.87	3.546%	$74.4185	$74.42	$74.40	$74.40
Purchase #7	$132.90	10.839%	$147.305	$147.31	$147.30	$147.30
7 purchase totals =	$748.88		$822.5848	$822.60	$822.55	$822.50