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	$149.76	5.852%	$158.524	$158.52	$158.50	$158.50
Purchase #2	$245.97	11.491%	$274.2344	$274.23	$274.25	$274.20
Purchase #3	$109.30	13.216%	$123.7451	$123.75	$123.75	$123.70
Purchase #4	$88.66	3.486%	$91.7507	$91.75	$91.75	$91.80
Purchase #5	$191.52	12.549%	$215.5538	$215.55	$215.55	$215.60
Purchase #6	$22.88	12.834%	$25.8164	$25.82	$25.80	$25.80
Purchase #7	$131.62	6.821%	$140.5978	$140.60	$140.60	$140.60
7 purchase totals =	$939.71		$1,030.2222	$1,030.22	$1,030.20	$1,030.20