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	$37.28	3.546%	$38.6019	$38.60	$38.60	$38.60
Purchase #2	$80.83	7.366%	$86.7839	$86.78	$86.80	$86.80
Purchase #3	$115.59	13.245%	$130.8999	$130.90	$130.90	$130.90
Purchase #4	$31.61	12.216%	$35.4715	$35.47	$35.45	$35.50
Purchase #5	$121.37	12.531%	$136.5789	$136.58	$136.60	$136.60
Purchase #6	$106.86	13.844%	$121.6537	$121.65	$121.65	$121.70
Purchase #7	$138.31	8.782%	$150.4564	$150.46	$150.45	$150.50
7 purchase totals =	$631.85		$700.4462	$700.44	$700.45	$700.60