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	$168.83	6.620%	$180.0065	$180.01	$180.00	$180.00
Purchase #2	$173.71	5.300%	$182.9166	$182.92	$182.90	$182.90
Purchase #3	$33.30	11.332%	$37.0736	$37.07	$37.05	$37.10
Purchase #4	$178.27	11.836%	$199.37	$199.37	$199.35	$199.40
Purchase #5	$123.52	12.709%	$139.2182	$139.22	$139.20	$139.20
Purchase #6	$81.93	6.111%	$86.9367	$86.94	$86.95	$86.90
Purchase #7	$144.27	10.221%	$159.0158	$159.02	$159.00	$159.00
7 purchase totals =	$903.83		$984.5374	$984.55	$984.45	$984.50