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	$146.86	13.249%	$166.3175	$166.32	$166.30	$166.30
Purchase #2	$129.78	3.852%	$134.7791	$134.78	$134.80	$134.80
Purchase #3	$95.53	4.771%	$100.0877	$100.09	$100.10	$100.10
Purchase #4	$149.89	13.473%	$170.0847	$170.08	$170.10	$170.10
Purchase #5	$64.34	12.315%	$72.2635	$72.26	$72.25	$72.30
Purchase #6	$23.56	6.183%	$25.0167	$25.02	$25.00	$25.00
Purchase #7	$49.86	13.360%	$56.5213	$56.52	$56.50	$56.50
7 purchase totals =	$659.82		$725.0705	$725.07	$725.05	$725.10