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	$93.73	6.259%	$99.5966	$99.60	$99.60	$99.60
Purchase #2	$22.90	10.479%	$25.2997	$25.30	$25.30	$25.30
Purchase #3	$8.93	7.490%	$9.5989	$9.60	$9.60	$9.60
Purchase #4	$191.85	4.653%	$200.7768	$200.78	$200.80	$200.80
Purchase #5	$68.51	13.758%	$77.9356	$77.94	$77.95	$77.90
Purchase #6	$99.64	4.207%	$103.8319	$103.83	$103.85	$103.80
Purchase #7	$134.88	9.764%	$148.0497	$148.05	$148.05	$148.00
7 purchase totals =	$620.44		$665.0892	$665.10	$665.15	$665.00