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	$80.50	3.597%	$83.3956	$83.40	$83.40	$83.40
Purchase #2	$50.74	4.609%	$53.0786	$53.08	$53.10	$53.10
Purchase #3	$115.47	13.734%	$131.3286	$131.33	$131.35	$131.30
Purchase #4	$6.77	11.304%	$7.5353	$7.54	$7.55	$7.50
Purchase #5	$237.65	8.661%	$258.2329	$258.23	$258.25	$258.20
Purchase #6	$29.36	12.543%	$33.0426	$33.04	$33.05	$33.00
Purchase #7	$203.58	13.683%	$231.4359	$231.44	$231.45	$231.40
7 purchase totals =	$724.07		$798.0495	$798.06	$798.15	$797.90