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	$67.52	10.220%	$74.4205	$74.42	$74.40	$74.40
Purchase #2	$43.60	7.524%	$46.8805	$46.88	$46.90	$46.90
Purchase #3	$179.29	3.214%	$185.0524	$185.05	$185.05	$185.10
Purchase #4	$84.43	6.495%	$89.9137	$89.91	$89.90	$89.90
Purchase #5	$159.49	10.666%	$176.5012	$176.50	$176.50	$176.50
Purchase #6	$164.71	5.419%	$173.6356	$173.64	$173.65	$173.60
Purchase #7	$86.83	9.637%	$95.1978	$95.20	$95.20	$95.20
7 purchase totals =	$785.87		$841.6017	$841.60	$841.60	$841.60