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	$58.77	9.311%	$64.2421	$64.24	$64.25	$64.20
Purchase #2	$90.52	5.421%	$95.4271	$95.43	$95.45	$95.40
Purchase #3	$42.57	3.823%	$44.1975	$44.20	$44.20	$44.20
Purchase #4	$46.85	6.431%	$49.8629	$49.86	$49.85	$49.90
Purchase #5	$110.72	3.281%	$114.3527	$114.35	$114.35	$114.40
Purchase #6	$137.96	4.810%	$144.5959	$144.60	$144.60	$144.60
Purchase #7	$163.76	5.121%	$172.1461	$172.15	$172.15	$172.10
7 purchase totals =	$651.15		$684.8243	$684.83	$684.85	$684.80