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	$221.31	8.596%	$240.3338	$240.33	$240.35	$240.30
Purchase #2	$194.32	3.326%	$200.7831	$200.78	$200.80	$200.80
Purchase #3	$132.95	10.179%	$146.483	$146.48	$146.50	$146.50
Purchase #4	$108.79	9.770%	$119.4188	$119.42	$119.40	$119.40
Purchase #5	$5.39	13.408%	$6.1127	$6.11	$6.10	$6.10
Purchase #6	$111.53	10.706%	$123.4704	$123.47	$123.45	$123.50
Purchase #7	$16.69	7.579%	$17.9549	$17.95	$17.95	$18.00
7 purchase totals =	$790.98		$854.5567	$854.54	$854.55	$854.60