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	$36.87	8.726%	$40.0873	$40.09	$40.10	$40.10
Purchase #2	$168.89	13.590%	$191.8422	$191.84	$191.85	$191.80
Purchase #3	$204.41	11.166%	$227.2344	$227.23	$227.25	$227.20
Purchase #4	$48.76	4.701%	$51.0522	$51.05	$51.05	$51.10
Purchase #5	$180.94	8.585%	$196.4737	$196.47	$196.45	$196.50
Purchase #6	$39.63	5.257%	$41.7133	$41.71	$41.70	$41.70
Purchase #7	$99.62	12.427%	$111.9998	$112.00	$112.00	$112.00
7 purchase totals =	$779.12		$860.4029	$860.39	$860.40	$860.40