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	$11.78	4.625%	$12.3248	$12.32	$12.30	$12.30
Purchase #2	$68.31	5.667%	$72.1811	$72.18	$72.20	$72.20
Purchase #3	$146.73	9.149%	$160.1543	$160.15	$160.15	$160.20
Purchase #4	$30.64	6.872%	$32.7456	$32.75	$32.75	$32.70
Purchase #5	$96.64	4.599%	$101.0845	$101.08	$101.10	$101.10
Purchase #6	$27.55	12.445%	$30.9786	$30.98	$31.00	$31.00
Purchase #7	$144.66	6.710%	$154.3667	$154.37	$154.35	$154.40
7 purchase totals =	$526.31		$563.8356	$563.83	$563.85	$563.90