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	$147.46	7.412%	$158.3897	$158.39	$158.40	$158.40
Purchase #2	$221.87	9.447%	$242.8301	$242.83	$242.85	$242.80
Purchase #3	$242.51	6.617%	$258.5569	$258.56	$258.55	$258.60
Purchase #4	$202.36	12.593%	$227.8432	$227.84	$227.85	$227.80
Purchase #5	$172.35	6.679%	$183.8613	$183.86	$183.85	$183.90
Purchase #6	$209.72	7.462%	$225.3693	$225.37	$225.35	$225.40
Purchase #7	$127.59	4.223%	$132.9781	$132.98	$133.00	$133.00
7 purchase totals =	$1,323.86		$1,429.8286	$1,429.83	$1,429.85	$1,429.90