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	$79.29	5.383%	$83.5582	$83.56	$83.55	$83.60
Purchase #2	$131.58	5.725%	$139.113	$139.11	$139.10	$139.10
Purchase #3	$85.36	11.451%	$95.1346	$95.13	$95.15	$95.10
Purchase #4	$105.97	3.347%	$109.5168	$109.52	$109.50	$109.50
Purchase #5	$116.64	13.176%	$132.0085	$132.01	$132.00	$132.00
Purchase #6	$167.59	6.389%	$178.2973	$178.30	$178.30	$178.30
Purchase #7	$245.62	3.380%	$253.922	$253.92	$253.90	$253.90
7 purchase totals =	$932.05		$991.5504	$991.55	$991.50	$991.50