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	$25.87	6.308%	$27.5019	$27.50	$27.50	$27.50
Purchase #2	$158.48	3.706%	$164.3533	$164.35	$164.35	$164.40
Purchase #3	$54.56	8.229%	$59.0497	$59.05	$59.05	$59.00
Purchase #4	$40.59	10.528%	$44.8633	$44.86	$44.85	$44.90
Purchase #5	$204.59	4.181%	$213.1439	$213.14	$213.15	$213.10
Purchase #6	$166.53	4.842%	$174.5934	$174.59	$174.60	$174.60
Purchase #7	$219.96	11.246%	$244.6967	$244.70	$244.70	$244.70
7 purchase totals =	$870.58		$928.2022	$928.19	$928.20	$928.20