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	$84.67	9.708%	$92.8898	$92.89	$92.90	$92.90
Purchase #2	$108.72	13.519%	$123.4179	$123.42	$123.40	$123.40
Purchase #3	$248.83	3.374%	$257.2255	$257.23	$257.25	$257.20
Purchase #4	$100.64	13.434%	$114.16	$114.16	$114.15	$114.20
Purchase #5	$37.48	13.209%	$42.4307	$42.43	$42.45	$42.40
Purchase #6	$226.61	13.200%	$256.5225	$256.52	$256.50	$256.50
Purchase #7	$192.29	6.348%	$204.4966	$204.50	$204.50	$204.50
7 purchase totals =	$999.24		$1,091.1430	$1,091.15	$1,091.15	$1,091.10