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	$168.68	6.395%	$179.4671	$179.47	$179.45	$179.50
Purchase #2	$39.29	6.350%	$41.7849	$41.78	$41.80	$41.80
Purchase #3	$59.39	5.860%	$62.8703	$62.87	$62.85	$62.90
Purchase #4	$33.71	13.539%	$38.274	$38.27	$38.25	$38.30
Purchase #5	$202.91	6.509%	$216.1174	$216.12	$216.10	$216.10
Purchase #6	$119.69	7.516%	$128.6859	$128.69	$128.70	$128.70
Purchase #7	$183.84	3.794%	$190.8149	$190.81	$190.80	$190.80
7 purchase totals =	$807.51		$858.0145	$858.01	$857.95	$858.10