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	$81.31	6.519%	$86.6106	$86.61	$86.60	$86.60
Purchase #2	$117.47	8.504%	$127.4596	$127.46	$127.45	$127.50
Purchase #3	$102.44	6.231%	$108.823	$108.82	$108.80	$108.80
Purchase #4	$176.35	4.692%	$184.6243	$184.62	$184.60	$184.60
Purchase #5	$89.68	7.857%	$96.7262	$96.73	$96.75	$96.70
Purchase #6	$185.26	13.325%	$209.9459	$209.95	$209.95	$209.90
Purchase #7	$42.94	7.688%	$46.2412	$46.24	$46.25	$46.20
7 purchase totals =	$795.45		$860.4308	$860.43	$860.40	$860.30