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	$110.28	11.710%	$123.1938	$123.19	$123.20	$123.20
Purchase #2	$203.65	8.522%	$221.0051	$221.01	$221.00	$221.00
Purchase #3	$178.51	10.161%	$196.6484	$196.65	$196.65	$196.60
Purchase #4	$87.29	4.322%	$91.0627	$91.06	$91.05	$91.10
Purchase #5	$166.92	5.528%	$176.1473	$176.15	$176.15	$176.10
Purchase #6	$56.69	10.166%	$62.4531	$62.45	$62.45	$62.50
Purchase #7	$152.34	10.575%	$168.45	$168.45	$168.45	$168.50
7 purchase totals =	$955.68		$1,038.9604	$1,038.96	$1,038.95	$1,039.00