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	$50.98	12.171%	$57.1848	$57.18	$57.20	$57.20
Purchase #2	$78.31	5.293%	$82.4549	$82.45	$82.45	$82.50
Purchase #3	$158.53	12.613%	$178.5254	$178.53	$178.55	$178.50
Purchase #4	$115.53	4.228%	$120.4146	$120.41	$120.40	$120.40
Purchase #5	$175.70	8.526%	$190.6802	$190.68	$190.70	$190.70
Purchase #6	$75.86	12.831%	$85.5936	$85.59	$85.60	$85.60
Purchase #7	$42.65	4.847%	$44.7172	$44.72	$44.70	$44.70
7 purchase totals =	$697.56		$759.5707	$759.56	$759.60	$759.60