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	$25.31	8.401%	$27.4363	$27.44	$27.45	$27.40
Purchase #2	$129.69	7.161%	$138.9771	$138.98	$139.00	$139.00
Purchase #3	$39.74	6.615%	$42.3688	$42.37	$42.35	$42.40
Purchase #4	$89.82	12.285%	$100.8544	$100.85	$100.85	$100.90
Purchase #5	$130.58	4.740%	$136.7695	$136.77	$136.75	$136.80
Purchase #6	$131.62	10.459%	$145.3861	$145.39	$145.40	$145.40
Purchase #7	$70.53	8.637%	$76.6217	$76.62	$76.60	$76.60
7 purchase totals =	$617.29		$668.4139	$668.42	$668.40	$668.50