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	$80.43	12.235%	$90.2706	$90.27	$90.25	$90.30
Purchase #2	$146.65	11.559%	$163.6013	$163.60	$163.60	$163.60
Purchase #3	$64.76	6.262%	$68.8153	$68.82	$68.80	$68.80
Purchase #4	$161.30	4.296%	$168.2294	$168.23	$168.25	$168.20
Purchase #5	$165.45	8.151%	$178.9358	$178.94	$178.95	$178.90
Purchase #6	$103.58	9.671%	$113.5972	$113.60	$113.60	$113.60
Purchase #7	$197.55	11.150%	$219.5768	$219.58	$219.60	$219.60
7 purchase totals =	$919.72		$1,003.0264	$1,003.04	$1,003.05	$1,003.00