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	$135.91	13.423%	$154.1532	$154.15	$154.15	$154.20
Purchase #2	$70.82	10.765%	$78.4438	$78.44	$78.45	$78.40
Purchase #3	$241.83	9.451%	$264.6854	$264.69	$264.70	$264.70
Purchase #4	$96.77	11.459%	$107.8589	$107.86	$107.85	$107.90
Purchase #5	$145.26	13.340%	$164.6377	$164.64	$164.65	$164.60
Purchase #6	$206.75	10.521%	$228.5022	$228.50	$228.50	$228.50
Purchase #7	$51.56	10.244%	$56.8418	$56.84	$56.85	$56.80
7 purchase totals =	$948.90		$1,055.1230	$1,055.12	$1,055.15	$1,055.10