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	$233.48	9.436%	$255.5112	$255.51	$255.50	$255.50
Purchase #2	$237.28	9.421%	$259.6341	$259.63	$259.65	$259.60
Purchase #3	$37.54	12.579%	$42.2622	$42.26	$42.25	$42.30
Purchase #4	$242.30	8.572%	$263.07	$263.07	$263.05	$263.10
Purchase #5	$183.56	6.689%	$195.8383	$195.84	$195.85	$195.80
Purchase #6	$155.58	6.606%	$165.8576	$165.86	$165.85	$165.90
Purchase #7	$83.95	6.580%	$89.4739	$89.47	$89.45	$89.50
7 purchase totals =	$1,173.69		$1,271.6473	$1,271.64	$1,271.60	$1,271.70