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	$79.82	12.286%	$89.6267	$89.63	$89.65	$89.60
Purchase #2	$132.69	3.837%	$137.7813	$137.78	$137.80	$137.80
Purchase #3	$227.37	4.370%	$237.3061	$237.31	$237.30	$237.30
Purchase #4	$98.57	13.784%	$112.1569	$112.16	$112.15	$112.20
Purchase #5	$236.60	7.305%	$253.8836	$253.88	$253.90	$253.90
Purchase #6	$62.46	11.298%	$69.5167	$69.52	$69.50	$69.50
Purchase #7	$41.50	3.870%	$43.1061	$43.11	$43.10	$43.10
7 purchase totals =	$879.01		$943.3774	$943.39	$943.40	$943.40