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	$191.75	12.325%	$215.3832	$215.38	$215.40	$215.40
Purchase #2	$238.50	7.311%	$255.9367	$255.94	$255.95	$255.90
Purchase #3	$115.30	7.509%	$123.9579	$123.96	$123.95	$124.00
Purchase #4	$30.66	3.590%	$31.7607	$31.76	$31.75	$31.80
Purchase #5	$171.38	7.722%	$184.614	$184.61	$184.60	$184.60
Purchase #6	$42.53	8.772%	$46.2607	$46.26	$46.25	$46.30
Purchase #7	$147.65	8.337%	$159.9596	$159.96	$159.95	$160.00
7 purchase totals =	$937.77		$1,017.8728	$1,017.87	$1,017.85	$1,018.00