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	$18.92	9.265%	$20.6729	$20.67	$20.65	$20.70
Purchase #2	$100.30	11.354%	$111.6881	$111.69	$111.70	$111.70
Purchase #3	$82.64	12.757%	$93.1824	$93.18	$93.20	$93.20
Purchase #4	$46.34	10.302%	$51.1139	$51.11	$51.10	$51.10
Purchase #5	$162.43	10.372%	$179.2772	$179.28	$179.30	$179.30
Purchase #6	$169.31	10.394%	$186.9081	$186.91	$186.90	$186.90
Purchase #7	$216.34	5.470%	$228.1738	$228.17	$228.15	$228.20
7 purchase totals =	$796.28		$871.0164	$871.01	$871.00	$871.10