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	$59.48	12.506%	$66.9186	$66.92	$66.90	$66.90
Purchase #2	$240.84	8.838%	$262.1254	$262.13	$262.15	$262.10
Purchase #3	$25.46	8.785%	$27.6967	$27.70	$27.70	$27.70
Purchase #4	$156.41	7.324%	$167.8655	$167.87	$167.85	$167.90
Purchase #5	$248.87	9.348%	$272.1344	$272.13	$272.15	$272.10
Purchase #6	$128.71	10.596%	$142.3481	$142.35	$142.35	$142.30
Purchase #7	$79.62	12.481%	$89.5574	$89.56	$89.55	$89.60
7 purchase totals =	$939.39		$1,028.6461	$1,028.66	$1,028.65	$1,028.60