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	$75.50	7.852%	$81.4283	$81.43	$81.45	$81.40
Purchase #2	$179.39	5.592%	$189.4215	$189.42	$189.40	$189.40
Purchase #3	$158.67	8.611%	$172.3331	$172.33	$172.35	$172.30
Purchase #4	$224.41	6.248%	$238.4311	$238.43	$238.45	$238.40
Purchase #5	$49.80	12.365%	$55.9578	$55.96	$55.95	$56.00
Purchase #6	$199.27	9.323%	$217.8479	$217.85	$217.85	$217.80
Purchase #7	$116.91	3.163%	$120.6079	$120.61	$120.60	$120.60
7 purchase totals =	$1,003.95		$1,076.0276	$1,076.03	$1,076.05	$1,075.90