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	$37.46	10.802%	$41.5064	$41.51	$41.50	$41.50
Purchase #2	$69.41	3.722%	$71.9934	$71.99	$72.00	$72.00
Purchase #3	$106.76	10.742%	$118.2282	$118.23	$118.25	$118.20
Purchase #4	$6.47	5.197%	$6.8062	$6.81	$6.80	$6.80
Purchase #5	$40.98	6.354%	$43.5839	$43.58	$43.60	$43.60
Purchase #6	$17.54	5.864%	$18.5685	$18.57	$18.55	$18.60
Purchase #7	$206.54	10.453%	$228.1296	$228.13	$228.15	$228.10
7 purchase totals =	$485.16		$528.8162	$528.82	$528.85	$528.80