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	$145.80	3.191%	$150.4525	$150.45	$150.45	$150.50
Purchase #2	$40.45	8.246%	$43.7855	$43.79	$43.80	$43.80
Purchase #3	$206.69	4.358%	$215.6976	$215.70	$215.70	$215.70
Purchase #4	$27.63	6.521%	$29.4318	$29.43	$29.45	$29.40
Purchase #5	$165.44	8.688%	$179.8134	$179.81	$179.80	$179.80
Purchase #6	$88.60	13.374%	$100.4494	$100.45	$100.45	$100.40
Purchase #7	$55.88	5.842%	$59.1445	$59.14	$59.15	$59.10
7 purchase totals =	$730.49		$778.7747	$778.77	$778.80	$778.70