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	$174.79	12.152%	$196.0305	$196.03	$196.05	$196.00
Purchase #2	$250.36	11.831%	$279.9801	$279.98	$280.00	$280.00
Purchase #3	$119.82	7.311%	$128.58	$128.58	$128.60	$128.60
Purchase #4	$41.68	4.520%	$43.5639	$43.56	$43.55	$43.60
Purchase #5	$103.39	12.824%	$116.6487	$116.65	$116.65	$116.60
Purchase #6	$85.83	6.483%	$91.3944	$91.39	$91.40	$91.40
Purchase #7	$124.79	7.861%	$134.5997	$134.60	$134.60	$134.60
7 purchase totals =	$900.66		$990.7973	$990.79	$990.85	$990.80