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	$101.29	10.111%	$111.5314	$111.53	$111.55	$111.50
Purchase #2	$107.27	7.714%	$115.5448	$115.54	$115.55	$115.50
Purchase #3	$34.59	8.650%	$37.582	$37.58	$37.60	$37.60
Purchase #4	$250.36	6.589%	$266.8562	$266.86	$266.85	$266.90
Purchase #5	$35.92	6.498%	$38.2541	$38.25	$38.25	$38.30
Purchase #6	$170.30	4.440%	$177.8613	$177.86	$177.85	$177.90
Purchase #7	$106.51	12.618%	$119.9494	$119.95	$119.95	$119.90
7 purchase totals =	$806.24		$867.5792	$867.57	$867.60	$867.60