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	$240.71	10.641%	$266.324	$266.32	$266.30	$266.30
Purchase #2	$139.28	3.355%	$143.9528	$143.95	$143.95	$144.00
Purchase #3	$31.82	10.409%	$35.1321	$35.13	$35.15	$35.10
Purchase #4	$23.33	3.119%	$24.0577	$24.06	$24.05	$24.10
Purchase #5	$203.82	9.601%	$223.3888	$223.39	$223.40	$223.40
Purchase #6	$63.90	5.414%	$67.3595	$67.36	$67.35	$67.40
Purchase #7	$79.49	13.802%	$90.4612	$90.46	$90.45	$90.50
7 purchase totals =	$782.35		$850.6761	$850.67	$850.65	$850.80