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	$99.45	10.421%	$109.8137	$109.81	$109.80	$109.80
Purchase #2	$78.92	5.794%	$83.4926	$83.49	$83.50	$83.50
Purchase #3	$169.86	9.352%	$185.7453	$185.75	$185.75	$185.70
Purchase #4	$92.99	12.111%	$104.252	$104.25	$104.25	$104.30
Purchase #5	$115.99	4.715%	$121.4589	$121.46	$121.45	$121.50
Purchase #6	$215.99	3.362%	$223.2516	$223.25	$223.25	$223.30
Purchase #7	$49.42	6.446%	$52.6056	$52.61	$52.60	$52.60
7 purchase totals =	$822.62		$880.6197	$880.62	$880.60	$880.70