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	$71.63	12.145%	$80.3295	$80.33	$80.35	$80.30
Purchase #2	$200.61	11.535%	$223.7504	$223.75	$223.75	$223.80
Purchase #3	$46.73	6.648%	$49.8366	$49.84	$49.85	$49.80
Purchase #4	$116.69	4.202%	$121.5933	$121.59	$121.60	$121.60
Purchase #5	$185.54	3.813%	$192.6146	$192.61	$192.60	$192.60
Purchase #6	$146.29	10.855%	$162.1698	$162.17	$162.15	$162.20
Purchase #7	$78.94	13.809%	$89.8408	$89.84	$89.85	$89.80
7 purchase totals =	$846.43		$920.1350	$920.13	$920.15	$920.10