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	$29.51	11.410%	$32.8771	$32.88	$32.90	$32.90
Purchase #2	$54.81	4.639%	$57.3526	$57.35	$57.35	$57.40
Purchase #3	$90.75	8.622%	$98.5745	$98.57	$98.55	$98.60
Purchase #4	$91.39	13.346%	$103.5869	$103.59	$103.60	$103.60
Purchase #5	$43.69	5.414%	$46.0554	$46.06	$46.05	$46.10
Purchase #6	$207.77	9.275%	$227.0407	$227.04	$227.05	$227.00
Purchase #7	$233.41	6.386%	$248.3156	$248.32	$248.30	$248.30
7 purchase totals =	$751.33		$813.8028	$813.81	$813.80	$813.90