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	$80.63	12.131%	$90.4112	$90.41	$90.40	$90.40
Purchase #2	$77.51	9.739%	$85.0587	$85.06	$85.05	$85.10
Purchase #3	$82.90	9.617%	$90.8725	$90.87	$90.85	$90.90
Purchase #4	$137.38	4.829%	$144.0141	$144.01	$144.00	$144.00
Purchase #5	$216.96	7.763%	$233.8026	$233.80	$233.80	$233.80
Purchase #6	$208.38	7.370%	$223.7376	$223.74	$223.75	$223.70
Purchase #7	$79.50	11.657%	$88.7673	$88.77	$88.75	$88.80
7 purchase totals =	$883.26		$956.6640	$956.66	$956.60	$956.70