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	$55.32	6.615%	$58.9794	$58.98	$59.00	$59.00
Purchase #2	$48.96	7.849%	$52.8029	$52.80	$52.80	$52.80
Purchase #3	$83.80	8.258%	$90.7202	$90.72	$90.70	$90.70
Purchase #4	$103.41	5.712%	$109.3168	$109.32	$109.30	$109.30
Purchase #5	$8.88	10.149%	$9.7812	$9.78	$9.80	$9.80
Purchase #6	$166.85	7.276%	$178.99	$178.99	$179.00	$179.00
Purchase #7	$64.62	12.225%	$72.5198	$72.52	$72.50	$72.50
7 purchase totals =	$531.84		$573.1103	$573.11	$573.10	$573.10