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	$64.71	8.794%	$70.4006	$70.40	$70.40	$70.40
Purchase #2	$92.55	13.738%	$105.2645	$105.26	$105.25	$105.30
Purchase #3	$79.32	3.342%	$81.9709	$81.97	$81.95	$82.00
Purchase #4	$154.58	12.377%	$173.7124	$173.71	$173.70	$173.70
Purchase #5	$241.27	3.842%	$250.5396	$250.54	$250.55	$250.50
Purchase #6	$40.75	4.505%	$42.5858	$42.59	$42.60	$42.60
Purchase #7	$223.69	13.123%	$253.0448	$253.04	$253.05	$253.00
7 purchase totals =	$896.87		$977.5186	$977.51	$977.50	$977.50