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	$212.58	13.256%	$240.7596	$240.76	$240.75	$240.80
Purchase #2	$181.29	5.874%	$191.939	$191.94	$191.95	$191.90
Purchase #3	$95.28	10.738%	$105.5112	$105.51	$105.50	$105.50
Purchase #4	$227.98	6.398%	$242.5662	$242.57	$242.55	$242.60
Purchase #5	$143.60	10.340%	$158.4482	$158.45	$158.45	$158.40
Purchase #6	$237.63	11.299%	$264.4798	$264.48	$264.50	$264.50
Purchase #7	$175.62	8.640%	$190.7936	$190.79	$190.80	$190.80
7 purchase totals =	$1,273.98		$1,394.4976	$1,394.50	$1,394.50	$1,394.50