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	$5.96	13.849%	$6.7854	$6.79	$6.80	$6.80
Purchase #2	$162.43	11.196%	$180.6157	$180.62	$180.60	$180.60
Purchase #3	$157.62	11.118%	$175.1442	$175.14	$175.15	$175.10
Purchase #4	$56.70	5.723%	$59.9449	$59.94	$59.95	$59.90
Purchase #5	$33.44	4.697%	$35.0107	$35.01	$35.00	$35.00
Purchase #6	$164.41	13.439%	$186.5051	$186.51	$186.50	$186.50
Purchase #7	$18.69	9.401%	$20.447	$20.45	$20.45	$20.40
7 purchase totals =	$599.25		$664.4530	$664.46	$664.45	$664.30