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	$71.44	11.782%	$79.8571	$79.86	$79.85	$79.90
Purchase #2	$137.58	10.277%	$151.7191	$151.72	$151.70	$151.70
Purchase #3	$218.75	10.536%	$241.7975	$241.80	$241.80	$241.80
Purchase #4	$66.87	5.807%	$70.7531	$70.75	$70.75	$70.80
Purchase #5	$40.54	5.724%	$42.8605	$42.86	$42.85	$42.90
Purchase #6	$236.76	13.688%	$269.1677	$269.17	$269.15	$269.20
Purchase #7	$145.61	7.752%	$156.8977	$156.90	$156.90	$156.90
7 purchase totals =	$917.55		$1,013.0527	$1,013.06	$1,013.00	$1,013.20