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	$179.40	6.540%	$191.1328	$191.13	$191.15	$191.10
Purchase #2	$19.34	11.531%	$21.5701	$21.57	$21.55	$21.60
Purchase #3	$19.50	3.695%	$20.2205	$20.22	$20.20	$20.20
Purchase #4	$61.95	13.687%	$70.4291	$70.43	$70.45	$70.40
Purchase #5	$230.64	5.493%	$243.3091	$243.31	$243.30	$243.30
Purchase #6	$19.63	8.856%	$21.3684	$21.37	$21.35	$21.40
Purchase #7	$246.33	13.771%	$280.2521	$280.25	$280.25	$280.30
7 purchase totals =	$776.79		$848.2821	$848.28	$848.25	$848.30