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	$166.38	11.269%	$185.1294	$185.13	$185.15	$185.10
Purchase #2	$47.46	13.870%	$54.0427	$54.04	$54.05	$54.00
Purchase #3	$205.63	12.320%	$230.9636	$230.96	$230.95	$231.00
Purchase #4	$155.91	9.601%	$170.8789	$170.88	$170.90	$170.90
Purchase #5	$176.49	6.421%	$187.8224	$187.82	$187.80	$187.80
Purchase #6	$209.75	5.746%	$221.8022	$221.80	$221.80	$221.80
Purchase #7	$82.92	9.522%	$90.8156	$90.82	$90.80	$90.80
7 purchase totals =	$1,044.54		$1,141.4548	$1,141.45	$1,141.45	$1,141.40