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	$248.67	12.765%	$280.4127	$280.41	$280.40	$280.40
Purchase #2	$36.35	4.474%	$37.9763	$37.98	$38.00	$38.00
Purchase #3	$183.36	6.239%	$194.7998	$194.80	$194.80	$194.80
Purchase #4	$86.66	12.468%	$97.4648	$97.46	$97.45	$97.50
Purchase #5	$204.25	10.487%	$225.6697	$225.67	$225.65	$225.70
Purchase #6	$67.45	6.290%	$71.6926	$71.69	$71.70	$71.70
Purchase #7	$228.52	6.163%	$242.6037	$242.60	$242.60	$242.60
7 purchase totals =	$1,055.26		$1,150.6196	$1,150.61	$1,150.60	$1,150.70