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	$152.58	9.236%	$166.6723	$166.67	$166.65	$166.70
Purchase #2	$167.90	8.820%	$182.7088	$182.71	$182.70	$182.70
Purchase #3	$125.37	12.517%	$141.0626	$141.06	$141.05	$141.10
Purchase #4	$28.49	4.773%	$29.8498	$29.85	$29.85	$29.80
Purchase #5	$79.54	12.863%	$89.7712	$89.77	$89.75	$89.80
Purchase #6	$244.89	6.403%	$260.5703	$260.57	$260.55	$260.60
Purchase #7	$148.39	12.860%	$167.473	$167.47	$167.45	$167.50
7 purchase totals =	$947.16		$1,038.1080	$1,038.10	$1,038.00	$1,038.20