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	$73.80	6.606%	$78.6752	$78.68	$78.70	$78.70
Purchase #2	$112.46	6.453%	$119.717	$119.72	$119.70	$119.70
Purchase #3	$33.40	12.367%	$37.5306	$37.53	$37.55	$37.50
Purchase #4	$235.79	8.465%	$255.7496	$255.75	$255.75	$255.70
Purchase #5	$181.86	4.485%	$190.0164	$190.02	$190.00	$190.00
Purchase #6	$121.87	8.385%	$132.0888	$132.09	$132.10	$132.10
Purchase #7	$109.43	12.412%	$123.0125	$123.01	$123.00	$123.00
7 purchase totals =	$868.61		$936.7901	$936.80	$936.80	$936.70