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	$47.92	7.553%	$51.5394	$51.54	$51.55	$51.50
Purchase #2	$68.79	13.418%	$78.0202	$78.02	$78.00	$78.00
Purchase #3	$221.65	12.330%	$248.9794	$248.98	$249.00	$249.00
Purchase #4	$11.69	13.486%	$13.2665	$13.27	$13.25	$13.30
Purchase #5	$89.30	11.689%	$99.7383	$99.74	$99.75	$99.70
Purchase #6	$246.25	4.174%	$256.5285	$256.53	$256.55	$256.50
Purchase #7	$180.90	9.559%	$198.1922	$198.19	$198.20	$198.20
7 purchase totals =	$866.50		$946.2645	$946.27	$946.30	$946.20