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	$171.72	5.765%	$181.6197	$181.62	$181.60	$181.60
Purchase #2	$123.49	13.713%	$140.4242	$140.42	$140.40	$140.40
Purchase #3	$237.47	4.801%	$248.8709	$248.87	$248.85	$248.90
Purchase #4	$166.76	12.201%	$187.1064	$187.11	$187.10	$187.10
Purchase #5	$127.84	8.800%	$139.0899	$139.09	$139.10	$139.10
Purchase #6	$109.55	13.159%	$123.9657	$123.97	$123.95	$124.00
Purchase #7	$227.47	3.109%	$234.542	$234.54	$234.55	$234.50
7 purchase totals =	$1,164.30		$1,255.6188	$1,255.62	$1,255.55	$1,255.60