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	$85.45	6.401%	$90.9197	$90.92	$90.90	$90.90
Purchase #2	$85.53	4.724%	$89.5704	$89.57	$89.55	$89.60
Purchase #3	$219.39	10.631%	$242.7134	$242.71	$242.70	$242.70
Purchase #4	$150.46	3.282%	$155.3981	$155.40	$155.40	$155.40
Purchase #5	$47.30	10.261%	$52.1535	$52.15	$52.15	$52.20
Purchase #6	$148.99	13.816%	$169.5745	$169.57	$169.55	$169.60
Purchase #7	$38.45	5.651%	$40.6228	$40.62	$40.60	$40.60
7 purchase totals =	$775.57		$840.9524	$840.94	$840.85	$841.00