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	$65.67	3.406%	$67.9067	$67.91	$67.90	$67.90
Purchase #2	$170.66	8.422%	$185.033	$185.03	$185.05	$185.00
Purchase #3	$182.43	3.428%	$188.6837	$188.68	$188.70	$188.70
Purchase #4	$19.28	12.638%	$21.7166	$21.72	$21.70	$21.70
Purchase #5	$132.51	4.372%	$138.3033	$138.30	$138.30	$138.30
Purchase #6	$46.52	11.539%	$51.8879	$51.89	$51.90	$51.90
Purchase #7	$30.33	6.716%	$32.367	$32.37	$32.35	$32.40
7 purchase totals =	$647.40		$685.8982	$685.90	$685.90	$685.90