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	$56.99	3.342%	$58.8946	$58.89	$58.90	$58.90
Purchase #2	$229.39	11.780%	$256.4121	$256.41	$256.40	$256.40
Purchase #3	$127.38	13.671%	$144.7941	$144.79	$144.80	$144.80
Purchase #4	$54.76	12.372%	$61.5349	$61.53	$61.55	$61.50
Purchase #5	$28.65	7.427%	$30.7778	$30.78	$30.80	$30.80
Purchase #6	$104.70	4.603%	$109.5193	$109.52	$109.50	$109.50
Purchase #7	$164.63	7.433%	$176.8669	$176.87	$176.85	$176.90
7 purchase totals =	$766.50		$838.7997	$838.79	$838.80	$838.80