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	$149.88	12.150%	$168.0904	$168.09	$168.10	$168.10
Purchase #2	$164.97	12.796%	$186.0796	$186.08	$186.10	$186.10
Purchase #3	$228.53	5.850%	$241.899	$241.90	$241.90	$241.90
Purchase #4	$83.25	5.770%	$88.0535	$88.05	$88.05	$88.10
Purchase #5	$12.75	6.819%	$13.6194	$13.62	$13.60	$13.60
Purchase #6	$78.88	9.380%	$86.2789	$86.28	$86.30	$86.30
Purchase #7	$198.29	10.158%	$218.4323	$218.43	$218.45	$218.40
7 purchase totals =	$916.55		$1,002.4531	$1,002.45	$1,002.50	$1,002.50