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	$234.44	10.374%	$258.7608	$258.76	$258.75	$258.80
Purchase #2	$38.36	3.474%	$39.6926	$39.69	$39.70	$39.70
Purchase #3	$138.83	4.621%	$145.2453	$145.25	$145.25	$145.20
Purchase #4	$52.82	12.868%	$59.6169	$59.62	$59.60	$59.60
Purchase #5	$99.72	13.195%	$112.8781	$112.88	$112.90	$112.90
Purchase #6	$78.91	13.647%	$89.6788	$89.68	$89.70	$89.70
Purchase #7	$44.95	12.571%	$50.6007	$50.60	$50.60	$50.60
7 purchase totals =	$688.03		$756.4732	$756.48	$756.50	$756.50