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	$72.85	8.202%	$78.8252	$78.83	$78.85	$78.80
Purchase #2	$230.96	5.663%	$244.0393	$244.04	$244.05	$244.00
Purchase #3	$64.82	9.113%	$70.727	$70.73	$70.75	$70.70
Purchase #4	$217.35	9.385%	$237.7483	$237.75	$237.75	$237.70
Purchase #5	$37.83	9.529%	$41.4348	$41.43	$41.45	$41.40
Purchase #6	$238.49	8.309%	$258.3061	$258.31	$258.30	$258.30
Purchase #7	$57.54	8.754%	$62.5771	$62.58	$62.60	$62.60
7 purchase totals =	$919.84		$993.6578	$993.67	$993.75	$993.50