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	$113.59	13.357%	$128.7622	$128.76	$128.75	$128.80
Purchase #2	$49.83	11.808%	$55.7139	$55.71	$55.70	$55.70
Purchase #3	$118.88	7.549%	$127.8543	$127.85	$127.85	$127.90
Purchase #4	$105.73	6.303%	$112.3942	$112.39	$112.40	$112.40
Purchase #5	$136.71	4.552%	$142.933	$142.93	$142.95	$142.90
Purchase #6	$127.68	4.538%	$133.4741	$133.47	$133.45	$133.50
Purchase #7	$109.74	10.107%	$120.8314	$120.83	$120.85	$120.80
7 purchase totals =	$762.16		$821.9631	$821.94	$821.95	$822.00