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	$18.33	11.521%	$20.4418	$20.44	$20.45	$20.40
Purchase #2	$243.65	4.699%	$255.0991	$255.10	$255.10	$255.10
Purchase #3	$110.93	6.599%	$118.2503	$118.25	$118.25	$118.30
Purchase #4	$151.31	3.789%	$157.0431	$157.04	$157.05	$157.00
Purchase #5	$134.67	3.647%	$139.5814	$139.58	$139.60	$139.60
Purchase #6	$197.32	9.142%	$215.359	$215.36	$215.35	$215.40
Purchase #7	$196.97	12.437%	$221.4672	$221.47	$221.45	$221.50
7 purchase totals =	$1,053.18		$1,127.2419	$1,127.24	$1,127.25	$1,127.30