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	$228.42	13.542%	$259.3526	$259.35	$259.35	$259.40
Purchase #2	$101.78	11.573%	$113.559	$113.56	$113.55	$113.60
Purchase #3	$130.99	5.452%	$138.1316	$138.13	$138.15	$138.10
Purchase #4	$128.85	4.345%	$134.4485	$134.45	$134.45	$134.40
Purchase #5	$148.34	4.518%	$155.042	$155.04	$155.05	$155.00
Purchase #6	$52.53	5.244%	$55.2847	$55.28	$55.30	$55.30
Purchase #7	$104.91	4.393%	$109.5187	$109.52	$109.50	$109.50
7 purchase totals =	$895.82		$965.3371	$965.33	$965.35	$965.30