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	$141.49	12.298%	$158.8904	$158.89	$158.90	$158.90
Purchase #2	$204.90	13.214%	$231.9755	$231.98	$232.00	$232.00
Purchase #3	$151.81	12.852%	$171.3206	$171.32	$171.30	$171.30
Purchase #4	$66.53	7.400%	$71.4532	$71.45	$71.45	$71.50
Purchase #5	$102.86	13.459%	$116.7039	$116.70	$116.70	$116.70
Purchase #6	$36.45	3.808%	$37.838	$37.84	$37.85	$37.80
Purchase #7	$248.73	13.291%	$281.7887	$281.79	$281.80	$281.80
7 purchase totals =	$952.77		$1,069.9703	$1,069.97	$1,070.00	$1,070.00