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	$239.95	3.280%	$247.8204	$247.82	$247.80	$247.80
Purchase #2	$68.92	11.395%	$76.7734	$76.77	$76.75	$76.80
Purchase #3	$200.91	12.662%	$226.3492	$226.35	$226.35	$226.30
Purchase #4	$29.84	5.342%	$31.4341	$31.43	$31.45	$31.40
Purchase #5	$121.50	5.309%	$127.9504	$127.95	$127.95	$128.00
Purchase #6	$62.92	7.196%	$67.4477	$67.45	$67.45	$67.40
Purchase #7	$86.29	3.234%	$89.0806	$89.08	$89.10	$89.10
7 purchase totals =	$810.33		$866.8558	$866.85	$866.85	$866.80