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	$53.32	3.313%	$55.0865	$55.09	$55.10	$55.10
Purchase #2	$28.82	7.487%	$30.9778	$30.98	$31.00	$31.00
Purchase #3	$16.28	13.198%	$18.4286	$18.43	$18.45	$18.40
Purchase #4	$103.50	10.467%	$114.3333	$114.33	$114.35	$114.30
Purchase #5	$38.79	9.169%	$42.3467	$42.35	$42.35	$42.30
Purchase #6	$181.55	13.198%	$205.511	$205.51	$205.50	$205.50
Purchase #7	$117.49	5.272%	$123.6841	$123.68	$123.70	$123.70
7 purchase totals =	$539.75		$590.3680	$590.37	$590.45	$590.30