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	$90.61	13.451%	$102.798	$102.80	$102.80	$102.80
Purchase #2	$154.90	10.836%	$171.685	$171.69	$171.70	$171.70
Purchase #3	$135.31	6.755%	$144.4502	$144.45	$144.45	$144.50
Purchase #4	$237.72	6.672%	$253.5807	$253.58	$253.60	$253.60
Purchase #5	$26.86	3.290%	$27.7437	$27.74	$27.75	$27.70
Purchase #6	$16.48	13.446%	$18.6959	$18.70	$18.70	$18.70
Purchase #7	$76.62	7.477%	$82.3489	$82.35	$82.35	$82.30
7 purchase totals =	$738.50		$801.3024	$801.31	$801.35	$801.30