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	$68.39	7.294%	$73.3784	$73.38	$73.40	$73.40
Purchase #2	$99.54	12.587%	$112.0691	$112.07	$112.05	$112.10
Purchase #3	$14.54	8.796%	$15.8189	$15.82	$15.80	$15.80
Purchase #4	$139.58	13.477%	$158.3912	$158.39	$158.40	$158.40
Purchase #5	$139.77	3.258%	$144.3237	$144.32	$144.30	$144.30
Purchase #6	$28.42	12.800%	$32.0578	$32.06	$32.05	$32.10
Purchase #7	$54.92	5.153%	$57.75	$57.75	$57.75	$57.80
7 purchase totals =	$545.16		$593.7891	$593.79	$593.75	$593.90