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	$95.89	8.448%	$103.9908	$103.99	$104.00	$104.00
Purchase #2	$89.80	11.705%	$100.3111	$100.31	$100.30	$100.30
Purchase #3	$81.95	10.493%	$90.549	$90.55	$90.55	$90.50
Purchase #4	$43.99	6.561%	$46.8762	$46.88	$46.90	$46.90
Purchase #5	$73.98	8.344%	$80.1529	$80.15	$80.15	$80.20
Purchase #6	$114.60	7.536%	$123.2363	$123.24	$123.25	$123.20
Purchase #7	$21.33	7.648%	$22.9613	$22.96	$22.95	$23.00
7 purchase totals =	$521.54		$568.0776	$568.08	$568.10	$568.10