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	$152.33	13.256%	$172.5229	$172.52	$172.50	$172.50
Purchase #2	$120.56	12.855%	$136.058	$136.06	$136.05	$136.10
Purchase #3	$40.73	7.823%	$43.9163	$43.92	$43.90	$43.90
Purchase #4	$68.96	6.766%	$73.6258	$73.63	$73.65	$73.60
Purchase #5	$219.39	10.493%	$242.4106	$242.41	$242.40	$242.40
Purchase #6	$189.88	9.857%	$208.5965	$208.60	$208.60	$208.60
Purchase #7	$94.29	7.126%	$101.0091	$101.01	$101.00	$101.00
7 purchase totals =	$886.14		$978.1392	$978.15	$978.10	$978.10