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	$122.28	12.500%	$137.565	$137.57	$137.55	$137.60
Purchase #2	$236.30	9.759%	$259.3605	$259.36	$259.35	$259.40
Purchase #3	$171.79	8.372%	$186.1723	$186.17	$186.15	$186.20
Purchase #4	$181.61	5.426%	$191.4642	$191.46	$191.45	$191.50
Purchase #5	$201.39	4.439%	$210.3297	$210.33	$210.35	$210.30
Purchase #6	$65.67	7.474%	$70.5782	$70.58	$70.60	$70.60
Purchase #7	$80.30	13.149%	$90.8586	$90.86	$90.85	$90.90
7 purchase totals =	$1,059.34		$1,146.3285	$1,146.33	$1,146.30	$1,146.50