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	$101.32	9.741%	$111.1896	$111.19	$111.20	$111.20
Purchase #2	$20.47	5.113%	$21.5166	$21.52	$21.50	$21.50
Purchase #3	$201.58	8.871%	$219.4622	$219.46	$219.45	$219.50
Purchase #4	$117.73	9.832%	$129.3052	$129.31	$129.30	$129.30
Purchase #5	$96.93	7.409%	$104.1115	$104.11	$104.10	$104.10
Purchase #6	$131.39	4.582%	$137.4103	$137.41	$137.40	$137.40
Purchase #7	$144.55	10.712%	$160.0342	$160.03	$160.05	$160.00
7 purchase totals =	$813.97		$883.0296	$883.03	$883.00	$883.00