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	$16.50	12.799%	$18.6118	$18.61	$18.60	$18.60
Purchase #2	$189.90	12.149%	$212.971	$212.97	$212.95	$213.00
Purchase #3	$212.32	13.525%	$241.0363	$241.04	$241.05	$241.00
Purchase #4	$100.66	11.666%	$112.403	$112.40	$112.40	$112.40
Purchase #5	$92.98	8.214%	$100.6174	$100.62	$100.60	$100.60
Purchase #6	$164.41	10.186%	$181.1568	$181.16	$181.15	$181.20
Purchase #7	$58.56	6.750%	$62.5128	$62.51	$62.50	$62.50
7 purchase totals =	$835.33		$929.3091	$929.31	$929.25	$929.30