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	$249.36	12.506%	$280.545	$280.55	$280.55	$280.50
Purchase #2	$206.65	4.661%	$216.282	$216.28	$216.30	$216.30
Purchase #3	$173.43	3.396%	$179.3197	$179.32	$179.30	$179.30
Purchase #4	$70.72	13.204%	$80.0579	$80.06	$80.05	$80.10
Purchase #5	$213.30	8.179%	$230.7458	$230.75	$230.75	$230.70
Purchase #6	$142.30	6.759%	$151.9181	$151.92	$151.90	$151.90
Purchase #7	$81.49	11.218%	$90.6315	$90.63	$90.65	$90.60
7 purchase totals =	$1,137.25		$1,229.5000	$1,229.51	$1,229.50	$1,229.40