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	$69.58	13.388%	$78.8954	$78.90	$78.90	$78.90
Purchase #2	$247.85	13.280%	$280.7645	$280.76	$280.75	$280.80
Purchase #3	$98.92	3.707%	$102.587	$102.59	$102.60	$102.60
Purchase #4	$130.85	9.455%	$143.2219	$143.22	$143.20	$143.20
Purchase #5	$66.35	5.413%	$69.9415	$69.94	$69.95	$69.90
Purchase #6	$149.93	3.297%	$154.8732	$154.87	$154.85	$154.90
Purchase #7	$6.29	4.837%	$6.5942	$6.59	$6.60	$6.60
7 purchase totals =	$769.77		$836.8777	$836.87	$836.85	$836.90