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	$241.32	10.190%	$265.9105	$265.91	$265.90	$265.90
Purchase #2	$147.25	5.141%	$154.8201	$154.82	$154.80	$154.80
Purchase #3	$233.93	5.786%	$247.4652	$247.47	$247.45	$247.50
Purchase #4	$231.44	12.724%	$260.8884	$260.89	$260.90	$260.90
Purchase #5	$164.31	10.483%	$181.5346	$181.53	$181.55	$181.50
Purchase #6	$249.93	7.289%	$268.1474	$268.15	$268.15	$268.10
Purchase #7	$90.85	9.244%	$99.2482	$99.25	$99.25	$99.20
7 purchase totals =	$1,359.03		$1,478.0144	$1,478.02	$1,478.00	$1,477.90