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	$94.81	12.431%	$106.5958	$106.60	$106.60	$106.60
Purchase #2	$209.32	5.722%	$221.2973	$221.30	$221.30	$221.30
Purchase #3	$51.33	6.409%	$54.6197	$54.62	$54.60	$54.60
Purchase #4	$98.26	11.775%	$109.8301	$109.83	$109.85	$109.80
Purchase #5	$137.36	5.345%	$144.7019	$144.70	$144.70	$144.70
Purchase #6	$104.53	7.683%	$112.561	$112.56	$112.55	$112.60
Purchase #7	$29.85	3.845%	$30.9977	$31.00	$31.00	$31.00
7 purchase totals =	$725.46		$780.6035	$780.61	$780.60	$780.60