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	$42.78	9.607%	$46.8899	$46.89	$46.90	$46.90
Purchase #2	$222.85	6.168%	$236.5954	$236.60	$236.60	$236.60
Purchase #3	$191.72	13.552%	$217.7019	$217.70	$217.70	$217.70
Purchase #4	$214.37	12.677%	$241.5457	$241.55	$241.55	$241.50
Purchase #5	$79.53	13.507%	$90.2721	$90.27	$90.25	$90.30
Purchase #6	$141.61	11.767%	$158.2732	$158.27	$158.25	$158.30
Purchase #7	$197.29	13.362%	$223.6519	$223.65	$223.65	$223.70
7 purchase totals =	$1,090.15		$1,214.9301	$1,214.93	$1,214.90	$1,215.00