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	$238.90	8.697%	$259.6771	$259.68	$259.70	$259.70
Purchase #2	$157.89	8.649%	$171.5459	$171.55	$171.55	$171.50
Purchase #3	$142.50	4.647%	$149.122	$149.12	$149.10	$149.10
Purchase #4	$239.56	13.341%	$271.5197	$271.52	$271.50	$271.50
Purchase #5	$66.72	6.497%	$71.0548	$71.05	$71.05	$71.10
Purchase #6	$20.60	3.470%	$21.3148	$21.31	$21.30	$21.30
Purchase #7	$56.89	5.187%	$59.8409	$59.84	$59.85	$59.80
7 purchase totals =	$923.06		$1,004.0752	$1,004.07	$1,004.05	$1,004.00