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	$250.91	11.682%	$280.2213	$280.22	$280.20	$280.20
Purchase #2	$142.48	11.114%	$158.3152	$158.32	$158.30	$158.30
Purchase #3	$242.76	11.337%	$270.2817	$270.28	$270.30	$270.30
Purchase #4	$56.75	10.296%	$62.593	$62.59	$62.60	$62.60
Purchase #5	$208.81	13.167%	$236.304	$236.30	$236.30	$236.30
Purchase #6	$230.70	10.614%	$255.1865	$255.19	$255.20	$255.20
Purchase #7	$22.85	7.271%	$24.5114	$24.51	$24.50	$24.50
7 purchase totals =	$1,155.26		$1,287.4131	$1,287.41	$1,287.40	$1,287.40