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	$45.95	13.847%	$52.3127	$52.31	$52.30	$52.30
Purchase #2	$53.36	10.686%	$59.062	$59.06	$59.05	$59.10
Purchase #3	$179.37	3.704%	$186.0139	$186.01	$186.00	$186.00
Purchase #4	$205.98	5.528%	$217.3666	$217.37	$217.35	$217.40
Purchase #5	$6.79	6.835%	$7.2541	$7.25	$7.25	$7.30
Purchase #6	$165.87	6.802%	$177.1525	$177.15	$177.15	$177.20
Purchase #7	$100.72	4.341%	$105.0923	$105.09	$105.10	$105.10
7 purchase totals =	$758.04		$804.2541	$804.24	$804.20	$804.40