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	$150.25	10.139%	$165.4838	$165.48	$165.50	$165.50
Purchase #2	$183.99	8.706%	$200.0082	$200.01	$200.00	$200.00
Purchase #3	$231.60	11.500%	$258.234	$258.23	$258.25	$258.20
Purchase #4	$116.85	13.488%	$132.6107	$132.61	$132.60	$132.60
Purchase #5	$204.51	8.333%	$221.5518	$221.55	$221.55	$221.60
Purchase #6	$247.88	7.419%	$266.2702	$266.27	$266.25	$266.30
Purchase #7	$126.85	7.430%	$136.275	$136.28	$136.30	$136.30
7 purchase totals =	$1,261.93		$1,380.4337	$1,380.43	$1,380.45	$1,380.50